diff --git a/backend/prisma/migrations/20261025_001_co_gestion/migration.sql b/backend/prisma/migrations/20261025_001_co_gestion/migration.sql
new file mode 100644
index 0000000..ef19a87
--- /dev/null
+++ b/backend/prisma/migrations/20261025_001_co_gestion/migration.sql
@@ -0,0 +1,32 @@
+-- Co-gestion d'un arbre (issue #145) : invitations du propriétaire. Migration additive, une table neuve.
+-- CreateTable
+CREATE TABLE "tree_invitations" (
+    "id" TEXT NOT NULL,
+    "treeId" TEXT NOT NULL,
+    "email" TEXT NOT NULL,
+    "tokenHash" TEXT NOT NULL,
+    "invitedByUserId" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "expiresAt" TIMESTAMP(3) NOT NULL,
+    "acceptedAt" TIMESTAMP(3),
+    "acceptedUserId" TEXT,
+    "revokedAt" TIMESTAMP(3),
+
+    CONSTRAINT "tree_invitations_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "tree_invitations_tokenHash_key" ON "tree_invitations"("tokenHash");
+
+-- CreateIndex
+CREATE INDEX "tree_invitations_treeId_idx" ON "tree_invitations"("treeId");
+
+-- CreateIndex
+CREATE INDEX "tree_invitations_email_idx" ON "tree_invitations"("email");
+
+-- AddForeignKey
+ALTER TABLE "tree_invitations" ADD CONSTRAINT "tree_invitations_treeId_fkey" FOREIGN KEY ("treeId") REFERENCES "trees"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "tree_invitations" ADD CONSTRAINT "tree_invitations_invitedByUserId_fkey" FOREIGN KEY ("invitedByUserId") REFERENCES "users"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
diff --git a/backend/prisma/schema.prisma b/backend/prisma/schema.prisma
index a6856a1..6d7fdaa 100644
--- a/backend/prisma/schema.prisma
+++ b/backend/prisma/schema.prisma
@@ -98,6 +98,7 @@ model User {
   reviewedContributionSessions  ContributionSession[] @relation("ContributionReviewedBy")
   treeVisits                    TreeVisit[]
   identities                    UserIdentity[]
+  sentTreeInvitations           TreeInvitation[]      @relation("TreeInvitationSentBy")
   lastOpenedTree                Tree?                 @relation("UserLastOpenedTree", fields: [lastOpenedTreeId], references: [id], onDelete: SetNull)
 
   @@index([lastOpenedAt])
@@ -146,6 +147,7 @@ model Tree {
   annotations          Annotation[]
   visits               TreeVisit[]
   lifeEvents           LifeEvent[]
+  invitations          TreeInvitation[]
   lastOpenedByUsers    User[]                @relation("UserLastOpenedTree")
 
   @@index([ownerUserId])
@@ -188,6 +190,28 @@ model TreeMembership {
   @@map("tree_memberships")
 }
 
+// Invitation à co-gérer un arbre (issue #145) : le propriétaire donne une adresse, Parenthèse un lien à transmettre.
+// Seule l'empreinte du jeton est gardée ; « Copier le lien » en tire un nouveau. Acceptée, elle donne le rôle admin
+// (co-gestionnaire). Le lien sert une fois, jusqu'à expiresAt.
+model TreeInvitation {
+  id              String    @id @default(cuid())
+  treeId          String
+  email           String
+  tokenHash       String    @unique
+  invitedByUserId String?
+  createdAt       DateTime  @default(now())
+  expiresAt       DateTime
+  acceptedAt      DateTime?
+  acceptedUserId  String?
+  revokedAt       DateTime?
+  tree            Tree      @relation(fields: [treeId], references: [id], onDelete: Cascade)
+  invitedBy       User?     @relation("TreeInvitationSentBy", fields: [invitedByUserId], references: [id], onDelete: SetNull)
+
+  @@index([treeId])
+  @@index([email])
+  @@map("tree_invitations")
+}
+
 model UserTreeAccess {
   id        String           @id @default(cuid())
   treeId    String
diff --git a/backend/src/app.ts b/backend/src/app.ts
index b47a640..d5d80d5 100644
--- a/backend/src/app.ts
+++ b/backend/src/app.ts
@@ -13,6 +13,7 @@ import { authRoutes } from './routes/auth.js'
 import { contributionRoutes } from './routes/contributions.js'
 import { graphRoutes } from './routes/graph.js'
 import { immichRoutes } from './routes/immich.js'
+import { managerRoutes } from './routes/managers.js'
 import { mediaRoutes } from './routes/media.js'
 import { oidcRoutes } from './routes/oidc.js'
 import { publicRoutes } from './routes/public.js'
@@ -159,6 +160,7 @@ export function createApp() {
   app.register(gedcomRoutes)
   app.register(visitRoutes)
   app.register(immichRoutes)
+  app.register(managerRoutes)
 
   app.setErrorHandler((error: FastifyError | Error, request, reply) => {
     if (error instanceof Prisma.PrismaClientInitializationError) {
diff --git a/backend/src/lib/oidc.ts b/backend/src/lib/oidc.ts
index 12a7798..69da4d7 100644
--- a/backend/src/lib/oidc.ts
+++ b/backend/src/lib/oidc.ts
@@ -50,9 +50,10 @@ export function appBaseUrl(): string {
   return (env.OIDC_APP_URL || new URL(env.OIDC_REDIRECT_URI).origin).replace(/\/$/, '')
 }
 
-// Seules la racine et l'adresse d'un arbre partagé sont acceptées comme retour : pas de redirection ouverte
+// Seules la racine, l'adresse d'un arbre partagé et celle d'une invitation à co-gérer un arbre sont acceptées
+// comme retour : pas de redirection ouverte
 export function safeReturnTo(value: unknown): string {
-  return typeof value === 'string' && /^\/(arbre\/[A-Za-z0-9-]{3,64})?$/.test(value) ? value : '/'
+  return typeof value === 'string' && /^\/(arbre\/[A-Za-z0-9-]{3,64}|invitation\/[A-Za-z0-9_-]{20,100})?$/.test(value) ? value : '/'
 }
 
 export async function startAuthorization(returnTo: string): Promise<{ url: URL; pending: OidcPending }> {
diff --git a/backend/src/lib/registration.ts b/backend/src/lib/registration.ts
index dc98371..9b037ee 100644
--- a/backend/src/lib/registration.ts
+++ b/backend/src/lib/registration.ts
@@ -12,11 +12,14 @@ export async function isRegistrationOpen(prisma: PrismaClient): Promise<boolean>
 // Seul chemin de création d'un compte. Inscription fermée : le compte n'est créé que si la base n'en a aucun,
 // sous un verrou de transaction pour que deux inscriptions simultanées sur une instance neuve n'en créent pas
 // deux. Renvoie null quand la création est refusée.
+// invited : l'appelant a vérifié une invitation à co-gérer un arbre pour cette adresse (issue #145) ; le
+// propriétaire de l'arbre a été admis par l'admin du serveur, son invitation ouvre un compte.
 export async function createAccountIfAllowed<T>(
   prisma: PrismaClient,
   create: (tx: Prisma.TransactionClient) => Promise<T>,
+  { invited = false }: { invited?: boolean } = {},
 ): Promise<T | null> {
-  if (env.ALLOW_REGISTRATION) return create(prisma)
+  if (env.ALLOW_REGISTRATION || invited) return create(prisma)
 
   return prisma.$transaction(async (tx) => {
     // Clé arbitraire, propre à la création de compte. pg_advisory_xact_lock renvoie void : $executeRaw, pas $queryRaw.
diff --git a/backend/src/lib/tree-invitations.ts b/backend/src/lib/tree-invitations.ts
new file mode 100644
index 0000000..d96ac70
--- /dev/null
+++ b/backend/src/lib/tree-invitations.ts
@@ -0,0 +1,116 @@
+import { createHash, randomBytes } from 'node:crypto'
+
+import type { Prisma, PrismaClient } from '@prisma/client'
+
+// Co-gestion d'un arbre (issue #145). Le propriétaire invite une adresse ; Parenthèse n'envoie pas de mail, il
+// donne un lien à transmettre. Seule l'empreinte du jeton est gardée en base.
+//
+// Qui est rattaché, et comment :
+// - par le lien, avec un compte à la même adresse (mot de passe ou OIDC). L'inscription par mot de passe ne
+//   vérifie pas l'adresse : le lien est la preuve, l'adresse seule ne suffit jamais ;
+// - sans le lien, seulement par OIDC, quand le fournisseur dit l'email vérifié (claimInvitationsForVerifiedEmail).
+
+export const INVITATION_TTL_MS = 14 * 24 * 60 * 60 * 1000
+export const MAX_PENDING_INVITATIONS = 20
+
+type Db = PrismaClient | Prisma.TransactionClient
+
+export function newInvitationToken(): { token: string; tokenHash: string } {
+  const token = randomBytes(32).toString('base64url')
+  return { token, tokenHash: hashInvitationToken(token) }
+}
+
+export function hashInvitationToken(token: string): string {
+  return createHash('sha256').update(token).digest('hex')
+}
+
+export function normalizeEmail(email: string): string {
+  return email.trim().toLowerCase()
+}
+
+// Invitation encore valable : ni acceptée, ni annulée, ni expirée
+export function pendingInvitationWhere(now = new Date()): Prisma.TreeInvitationWhereInput {
+  return { acceptedAt: null, revokedAt: null, expiresAt: { gt: now }, tree: { deletedAt: null } }
+}
+
+export async function findPendingInvitationByToken(db: Db, token: string) {
+  if (!token || token.length > 200) return null
+  return db.treeInvitation.findFirst({
+    where: { tokenHash: hashInvitationToken(token), ...pendingInvitationWhere() },
+    include: { tree: { select: { id: true, name: true, ownerUserId: true, owner: { select: { firstName: true } } } } },
+  })
+}
+
+export async function hasPendingInvitationForEmail(db: Db, email: string): Promise<boolean> {
+  const found = await db.treeInvitation.findFirst({ where: { email: normalizeEmail(email), ...pendingInvitationWhere() }, select: { id: true } })
+  return Boolean(found)
+}
+
+export type AcceptResult = { ok: true; treeId: string } | { ok: false; error: 'invitation_invalid' | 'invitation_email_mismatch' | 'already_owner' }
+
+// Accepte une invitation pour ce compte : co-gestionnaire (admin) de l'arbre. L'invitation ne sert qu'une fois,
+// même pour deux acceptations simultanées (updateMany conditionnel dans la transaction).
+export async function acceptInvitation(prisma: PrismaClient, invitationId: string, userId: string, userEmail: string): Promise<AcceptResult> {
+  return prisma.$transaction(async (tx) => {
+    const invitation = await tx.treeInvitation.findFirst({
+      where: { id: invitationId, ...pendingInvitationWhere() },
+      select: { id: true, treeId: true, email: true, tree: { select: { ownerUserId: true } } },
+    })
+    if (!invitation) return { ok: false, error: 'invitation_invalid' } as const
+    if (normalizeEmail(userEmail) !== invitation.email) return { ok: false, error: 'invitation_email_mismatch' } as const
+    if (invitation.tree.ownerUserId === userId) return { ok: false, error: 'already_owner' } as const
+
+    const claimed = await tx.treeInvitation.updateMany({
+      where: { id: invitation.id, ...pendingInvitationWhere() },
+      data: { acceptedAt: new Date(), acceptedUserId: userId },
+    })
+    if (claimed.count !== 1) return { ok: false, error: 'invitation_invalid' } as const
+
+    const existing = await tx.treeMembership.findUnique({
+      where: { treeId_userId: { treeId: invitation.treeId, userId } },
+      select: { role: true },
+    })
+    if (!existing) {
+      await tx.treeMembership.create({ data: { treeId: invitation.treeId, userId, role: 'admin' } })
+    } else if (existing.role === 'member') {
+      await tx.treeMembership.update({ where: { treeId_userId: { treeId: invitation.treeId, userId } }, data: { role: 'admin' } })
+    }
+    // L'arbre s'ouvre à la prochaine visite
+    await tx.user.update({
+      where: { id: userId },
+      data: { lastOpenedTreeId: invitation.treeId, lastOpenedAccessMode: 'member', lastOpenedRole: 'admin', lastOpenedAt: new Date() },
+    })
+    await tx.auditLog.create({
+      data: {
+        treeId: invitation.treeId,
+        actorType: 'user',
+        actorId: userId,
+        action: 'manager_joined',
+        entityType: 'tree',
+        entityId: invitation.treeId,
+        payloadJson: { invitationId: invitation.id },
+      },
+    })
+    return { ok: true, treeId: invitation.treeId } as const
+  })
+}
+
+// Connexion OIDC avec un email vérifié par le fournisseur : les invitations en attente à cette adresse sont
+// acceptées sans le lien. Jamais pour un email non vérifié, jamais pour une connexion par mot de passe.
+export async function claimInvitationsForVerifiedEmail(prisma: PrismaClient, userId: string, verifiedEmail: string): Promise<string[]> {
+  const email = normalizeEmail(verifiedEmail)
+  const invitations = await prisma.treeInvitation.findMany({ where: { email, ...pendingInvitationWhere() }, select: { id: true } })
+  const joined: string[] = []
+  for (const invitation of invitations) {
+    const result = await acceptInvitation(prisma, invitation.id, userId, email)
+    if (result.ok) joined.push(result.treeId)
+  }
+  return joined
+}
+
+// « jacques@exemple.fr » devient « ja•••@exemple.fr » sur la page publique du lien
+export function maskEmail(email: string): string {
+  const [local, domain] = email.split('@')
+  if (!domain) return '•••'
+  return `${local.slice(0, Math.min(2, local.length))}•••@${domain}`
+}
diff --git a/backend/src/routes/auth.ts b/backend/src/routes/auth.ts
index 1499d9c..b8c21fd 100644
--- a/backend/src/routes/auth.ts
+++ b/backend/src/routes/auth.ts
@@ -6,6 +6,7 @@ import { env } from '../config/env.js'
 import { confirmsWithPassword, hashPassword, verifyPassword } from '../lib/auth.js'
 import { isOidcEnabled } from '../lib/oidc.js'
 import { createAccountIfAllowed, isRegistrationOpen } from '../lib/registration.js'
+import { acceptInvitation, findPendingInvitationByToken } from '../lib/tree-invitations.js'
 import { signUserSession } from '../lib/user-session.js'
 import { revokeUserToken } from '../lib/token-revocation.js'
 import { deletedAccountVisitorKey } from '../lib/tree-visits.js'
@@ -27,6 +28,8 @@ const credentialsSchema = z.object({
 // Prénom du compte, facultatif : seulement à l'inscription (la connexion ne le demande pas)
 const registerSchema = credentialsSchema.extend({
   firstName: z.string().max(60).optional().nullable(),
+  // Lien d'invitation à co-gérer un arbre : ouvre un compte même inscription fermée, à l'adresse invitée seulement
+  invitationToken: z.string().min(1).max(200).optional(),
 })
 
 function trimmedFirstName(value: string | null | undefined): string | null {
@@ -134,12 +137,20 @@ export const authRoutes: FastifyPluginAsync = async (app) => {
         return reply.code(403).send({ error: 'password_login_disabled' })
       }
 
+      const email = parsed.data.email.trim().toLowerCase()
+      const invitation = parsed.data.invitationToken ? await findPendingInvitationByToken(app.prisma, parsed.data.invitationToken) : null
+      if (parsed.data.invitationToken && !invitation) {
+        return reply.code(410).send({ error: 'invitation_invalid' })
+      }
+      if (invitation && invitation.email !== email) {
+        return reply.code(403).send({ error: 'invitation_email_mismatch' })
+      }
+
       // Inscription fermée : refusée avant toute lecture, la réponse ne dit pas si l'adresse a un compte
-      if (!(await isRegistrationOpen(app.prisma))) {
+      if (!invitation && !(await isRegistrationOpen(app.prisma))) {
         return reply.code(403).send({ error: 'registration_closed' })
       }
 
-      const email = parsed.data.email.trim().toLowerCase()
       const existing = await app.prisma.user.findUnique({ where: { email } })
       if (existing) {
         return reply.code(409).send({ error: 'email_already_exists' })
@@ -157,13 +168,20 @@ export const authRoutes: FastifyPluginAsync = async (app) => {
           email: true,
           firstName: true,
         },
-      }))
+      }), { invited: Boolean(invitation) })
       // Un autre compte est né pendant le calcul du hash, sur une instance fermée
       if (!user) {
         return reply.code(403).send({ error: 'registration_closed' })
       }
 
-      return reply.code(201).send({ token: signUserSession(app, user), user: { ...user, hasPassword: true } })
+      // Compte ouvert par une invitation : co-gestionnaire de l'arbre tout de suite
+      let joinedTreeId: string | null = null
+      if (invitation) {
+        const accepted = await acceptInvitation(app.prisma, invitation.id, user.id, user.email)
+        if (accepted.ok) joinedTreeId = accepted.treeId
+      }
+
+      return reply.code(201).send({ token: signUserSession(app, user), user: { ...user, hasPassword: true }, joinedTreeId })
     },
   )
 
diff --git a/backend/src/routes/managers.ts b/backend/src/routes/managers.ts
new file mode 100644
index 0000000..a627f77
--- /dev/null
+++ b/backend/src/routes/managers.ts
@@ -0,0 +1,221 @@
+import type { FastifyInstance, FastifyPluginAsync, FastifyReply, FastifyRequest } from 'fastify'
+import { z } from 'zod'
+
+import { env } from '../config/env.js'
+import { isOidcEnabled } from '../lib/oidc.js'
+import {
+  INVITATION_TTL_MS,
+  MAX_PENDING_INVITATIONS,
+  acceptInvitation,
+  findPendingInvitationByToken,
+  maskEmail,
+  newInvitationToken,
+  normalizeEmail,
+  pendingInvitationWhere,
+} from '../lib/tree-invitations.js'
+
+// Co-gestion d'un arbre (issue #145). Un co-gestionnaire est un membre « admin » : il fait tout ce que fait le
+// propriétaire, sauf inviter ou retirer un co-gestionnaire et supprimer l'arbre (DELETE /trees/:id, réservé au
+// propriétaire). Les droits sont relus en base à chaque requête : un co-gestionnaire retiré perd la main aussitôt.
+
+const treeIdParamSchema = z.object({ id: z.string().min(1) })
+const invitationParamsSchema = z.object({ id: z.string().min(1), invitationId: z.string().min(1) })
+const managerParamsSchema = z.object({ id: z.string().min(1), userId: z.string().min(1) })
+const tokenParamSchema = z.object({ token: z.string().min(1).max(200) })
+const inviteSchema = z.object({ email: z.string().trim().email().max(254) })
+
+function requireUser(request: FastifyRequest, reply: FastifyReply): { userId: string } | null {
+  if (!request.actor || request.actor.kind !== 'user') {
+    reply.code(401).send({ error: 'authentication_required' })
+    return null
+  }
+  return { userId: request.actor.userId }
+}
+
+async function membershipOf(app: FastifyInstance, treeId: string, userId: string) {
+  const membership = await app.prisma.treeMembership.findUnique({
+    where: { treeId_userId: { treeId, userId } },
+    select: { role: true, tree: { select: { deletedAt: true, ownerUserId: true } } },
+  })
+  return membership && !membership.tree.deletedAt ? membership : null
+}
+
+function audit(app: FastifyInstance, treeId: string, actorId: string, action: string, payloadJson: Record<string, string>) {
+  return app.prisma.auditLog.create({
+    data: { treeId, actorType: 'user', actorId, action, entityType: 'tree', entityId: treeId, payloadJson },
+  })
+}
+
+export const managerRoutes: FastifyPluginAsync = async (app) => {
+  // Gestionnaires et invitations en attente, pour tout gestionnaire de l'arbre. canManage : le propriétaire.
+  app.get('/trees/:id/managers', async (request, reply) => {
+    const user = requireUser(request, reply)
+    if (!user) return
+    const params = treeIdParamSchema.safeParse(request.params)
+    if (!params.success) return reply.code(400).send({ error: 'invalid_tree_id' })
+
+    const membership = await membershipOf(app, params.data.id, user.userId)
+    if (!membership || (membership.role !== 'owner' && membership.role !== 'admin')) {
+      return reply.code(403).send({ error: 'forbidden' })
+    }
+
+    const [managers, invitations] = await Promise.all([
+      app.prisma.treeMembership.findMany({
+        where: { treeId: params.data.id, role: { in: ['owner', 'admin'] } },
+        select: { role: true, createdAt: true, user: { select: { id: true, email: true, firstName: true } } },
+        orderBy: { createdAt: 'asc' },
+      }),
+      app.prisma.treeInvitation.findMany({
+        where: { treeId: params.data.id, ...pendingInvitationWhere() },
+        select: { id: true, email: true, createdAt: true, expiresAt: true },
+        orderBy: { createdAt: 'asc' },
+      }),
+    ])
+
+    return reply.send({
+      canManage: membership.role === 'owner',
+      managers: managers.map((m) => ({ userId: m.user.id, email: m.user.email, firstName: m.user.firstName, role: m.role, since: m.createdAt })),
+      invitations,
+    })
+  })
+
+  // Inviter une adresse. Une invitation déjà en attente pour cette adresse reçoit un nouveau lien (l'ancien ne
+  // sert plus). Le jeton n'est rendu qu'ici et par /link : la base n'en garde que l'empreinte.
+  app.post('/trees/:id/invitations', { config: { rateLimit: { max: 20, timeWindow: '10 minutes' } } }, async (request, reply) => {
+    const user = requireUser(request, reply)
+    if (!user) return
+    const params = treeIdParamSchema.safeParse(request.params)
+    if (!params.success) return reply.code(400).send({ error: 'invalid_tree_id' })
+    const payload = inviteSchema.safeParse(request.body)
+    if (!payload.success) return reply.code(400).send({ error: 'invalid_email' })
+
+    const membership = await membershipOf(app, params.data.id, user.userId)
+    if (!membership || membership.role !== 'owner') return reply.code(403).send({ error: 'forbidden' })
+
+    const email = normalizeEmail(payload.data.email)
+    const alreadyManager = await app.prisma.treeMembership.findFirst({
+      where: { treeId: params.data.id, role: { in: ['owner', 'admin'] }, user: { email } },
+      select: { id: true },
+    })
+    if (alreadyManager) return reply.code(409).send({ error: 'already_manager' })
+
+    const { token, tokenHash } = newInvitationToken()
+    const expiresAt = new Date(Date.now() + INVITATION_TTL_MS)
+    const existing = await app.prisma.treeInvitation.findFirst({
+      where: { treeId: params.data.id, email, ...pendingInvitationWhere() },
+      select: { id: true },
+    })
+    let invitation
+    if (existing) {
+      invitation = await app.prisma.treeInvitation.update({
+        where: { id: existing.id },
+        data: { tokenHash, expiresAt },
+        select: { id: true, email: true, createdAt: true, expiresAt: true },
+      })
+    } else {
+      const pending = await app.prisma.treeInvitation.count({ where: { treeId: params.data.id, ...pendingInvitationWhere() } })
+      if (pending >= MAX_PENDING_INVITATIONS) return reply.code(429).send({ error: 'too_many_invitations' })
+      invitation = await app.prisma.treeInvitation.create({
+        data: { treeId: params.data.id, email, tokenHash, expiresAt, invitedByUserId: user.userId },
+        select: { id: true, email: true, createdAt: true, expiresAt: true },
+      })
+    }
+    await audit(app, params.data.id, user.userId, 'manager_invited', { invitationId: invitation.id })
+    return reply.code(201).send({ invitation, token })
+  })
+
+  // « Copier le lien » : un nouveau jeton (l'ancien lien ne sert plus), la durée repart de zéro
+  app.post('/trees/:id/invitations/:invitationId/link', { config: { rateLimit: { max: 30, timeWindow: '10 minutes' } } }, async (request, reply) => {
+    const user = requireUser(request, reply)
+    if (!user) return
+    const params = invitationParamsSchema.safeParse(request.params)
+    if (!params.success) return reply.code(400).send({ error: 'invalid_params' })
+
+    const membership = await membershipOf(app, params.data.id, user.userId)
+    if (!membership || membership.role !== 'owner') return reply.code(403).send({ error: 'forbidden' })
+
+    const { token, tokenHash } = newInvitationToken()
+    const updated = await app.prisma.treeInvitation.updateMany({
+      where: { id: params.data.invitationId, treeId: params.data.id, ...pendingInvitationWhere() },
+      data: { tokenHash, expiresAt: new Date(Date.now() + INVITATION_TTL_MS) },
+    })
+    if (updated.count !== 1) return reply.code(404).send({ error: 'invitation_not_found' })
+    return reply.send({ token })
+  })
+
+  app.delete('/trees/:id/invitations/:invitationId', async (request, reply) => {
+    const user = requireUser(request, reply)
+    if (!user) return
+    const params = invitationParamsSchema.safeParse(request.params)
+    if (!params.success) return reply.code(400).send({ error: 'invalid_params' })
+
+    const membership = await membershipOf(app, params.data.id, user.userId)
+    if (!membership || membership.role !== 'owner') return reply.code(403).send({ error: 'forbidden' })
+
+    const revoked = await app.prisma.treeInvitation.updateMany({
+      where: { id: params.data.invitationId, treeId: params.data.id, ...pendingInvitationWhere() },
+      data: { revokedAt: new Date() },
+    })
+    if (revoked.count !== 1) return reply.code(404).send({ error: 'invitation_not_found' })
+    await audit(app, params.data.id, user.userId, 'manager_invitation_revoked', { invitationId: params.data.invitationId })
+    return reply.send({ ok: true })
+  })
+
+  // Retirer un co-gestionnaire (le propriétaire), ou quitter la gestion (le co-gestionnaire lui-même).
+  // Le propriétaire ne se retire jamais : son arbre part avec lui (suppression de l'arbre ou du compte).
+  app.delete('/trees/:id/managers/:userId', async (request, reply) => {
+    const user = requireUser(request, reply)
+    if (!user) return
+    const params = managerParamsSchema.safeParse(request.params)
+    if (!params.success) return reply.code(400).send({ error: 'invalid_params' })
+
+    const membership = await membershipOf(app, params.data.id, user.userId)
+    const leaving = params.data.userId === user.userId
+    if (!membership || (leaving ? membership.role !== 'admin' : membership.role !== 'owner')) {
+      return reply.code(403).send({ error: 'forbidden' })
+    }
+
+    const removed = await app.prisma.treeMembership.deleteMany({
+      where: { treeId: params.data.id, userId: params.data.userId, role: 'admin' },
+    })
+    if (removed.count !== 1) return reply.code(404).send({ error: 'manager_not_found' })
+    await audit(app, params.data.id, user.userId, leaving ? 'manager_left' : 'manager_removed', { userId: params.data.userId })
+    return reply.send({ ok: true })
+  })
+
+  // Page du lien, sans compte : l'arbre, qui invite, l'adresse masquée, et les façons d'entrer sur ce serveur
+  app.get('/invitations/:token', { config: { rateLimit: { max: 30, timeWindow: '1 minute' } } }, async (request, reply) => {
+    const params = tokenParamSchema.safeParse(request.params)
+    if (!params.success) return reply.code(404).send({ error: 'invitation_invalid' })
+    const invitation = await findPendingInvitationByToken(app.prisma, params.data.token)
+    if (!invitation) return reply.code(404).send({ error: 'invitation_invalid' })
+    return reply.send({
+      treeName: invitation.tree.name,
+      invitedBy: invitation.tree.owner.firstName || null,
+      emailHint: maskEmail(invitation.email),
+      expiresAt: invitation.expiresAt,
+      passwordLogin: env.PASSWORD_LOGIN,
+      oidc: isOidcEnabled() ? { name: env.OIDC_PROVIDER_NAME } : null,
+    })
+  })
+
+  // Accepter avec le compte connecté : il doit avoir l'adresse invitée
+  app.post('/invitations/:token/accept', { config: { rateLimit: { max: 10, timeWindow: '1 minute' } } }, async (request, reply) => {
+    const user = requireUser(request, reply)
+    if (!user) return
+    const params = tokenParamSchema.safeParse(request.params)
+    if (!params.success) return reply.code(404).send({ error: 'invitation_invalid' })
+
+    const invitation = await findPendingInvitationByToken(app.prisma, params.data.token)
+    if (!invitation) return reply.code(404).send({ error: 'invitation_invalid' })
+    const account = await app.prisma.user.findUnique({ where: { id: user.userId }, select: { email: true } })
+    if (!account) return reply.code(401).send({ error: 'authentication_required' })
+
+    const result = await acceptInvitation(app.prisma, invitation.id, user.userId, account.email)
+    if (!result.ok) {
+      const code = result.error === 'invitation_invalid' ? 404 : result.error === 'already_owner' ? 409 : 403
+      return reply.code(code).send({ error: result.error })
+    }
+    return reply.send({ treeId: result.treeId, role: 'admin' })
+  })
+}
diff --git a/backend/src/routes/oidc.ts b/backend/src/routes/oidc.ts
index ef12b63..b12d023 100644
--- a/backend/src/routes/oidc.ts
+++ b/backend/src/routes/oidc.ts
@@ -15,6 +15,7 @@ import {
 } from '../lib/oidc.js'
 import { confirmsWithPassword } from '../lib/auth.js'
 import { createAccountIfAllowed } from '../lib/registration.js'
+import { claimInvitationsForVerifiedEmail, hasPendingInvitationForEmail } from '../lib/tree-invitations.js'
 import { signUserSession } from '../lib/user-session.js'
 
 // Parcours : /auth/oidc/start pose un cookie signé (state, nonce, vérificateur PKCE) et part chez le fournisseur ;
@@ -86,6 +87,7 @@ async function resolveAccount(app: FastifyInstance, identity: OidcIdentity): Pro
     return { userId: existing.id }
   }
 
+  // Une invitation à co-gérer un arbre ouvre un compte même inscription fermée, si le fournisseur garantit l'adresse
   const created = await createAccountIfAllowed(app.prisma, (tx) => tx.user.create({
     data: {
       email: identity.email as string,
@@ -94,7 +96,7 @@ async function resolveAccount(app: FastifyInstance, identity: OidcIdentity): Pro
       identities: { create: { issuer: identity.issuer, subject: identity.subject } },
     },
     select: { id: true },
-  }))
+  }), { invited: identity.emailVerified && await hasPendingInvitationForEmail(app.prisma, identity.email) })
   return created ? { userId: created.id } : { error: 'registration_closed' }
 }
 
@@ -179,6 +181,10 @@ export const oidcRoutes: FastifyPluginAsync = async (app) => {
       if ('error' in result) {
         return redirectToApp(reply, returnTo, `oidc_error=${result.error}`)
       }
+      // Invitations à co-gérer un arbre : acceptées sans le lien, l'adresse étant garantie par le fournisseur
+      if (identity.email && identity.emailVerified) {
+        await claimInvitationsForVerifiedEmail(app.prisma, result.userId, identity.email)
+      }
 
       const handoff = app.jwt.sign(
         { kind: 'oidc_handoff', sub: result.userId, jti: randomUUID() },
diff --git a/backend/src/routes/trees.ts b/backend/src/routes/trees.ts
index 41da55b..b3f4009 100644
--- a/backend/src/routes/trees.ts
+++ b/backend/src/routes/trees.ts
@@ -448,14 +448,29 @@ export const treeRoutes: FastifyPluginAsync = async (app) => {
       role: string
       accessMode: 'member' | 'share'
       lastAccessedAt: Date | null
+      coManagers?: string[]
     }> = []
 
+    // Co-gestionnaires des arbres possédés : l'écran de suppression du compte les nomme (l'arbre part avec le compte)
+    const ownedIds = memberships.filter((m: { role: string }) => m.role === 'owner').map((m: { tree: { id: string } }) => m.tree.id)
+    const coManagerRows = ownedIds.length
+      ? await app.prisma.treeMembership.findMany({
+          where: { treeId: { in: ownedIds }, role: 'admin' },
+          select: { treeId: true, user: { select: { firstName: true, email: true } } },
+        })
+      : []
+
     for (const membership of memberships) {
       mergedTrees.push({
         ...membership.tree,
         role: membership.role,
         accessMode: 'member',
         lastAccessedAt: null,
+        ...(membership.role === 'owner' ? {
+          coManagers: coManagerRows
+            .filter((row: { treeId: string }) => row.treeId === membership.tree.id)
+            .map((row: { user: { firstName: string | null; email: string } }) => row.user.firstName || row.user.email),
+        } : {}),
       })
     }
 
diff --git a/backend/test/co-gestion.db.test.ts b/backend/test/co-gestion.db.test.ts
new file mode 100644
index 0000000..abfb9d7
--- /dev/null
+++ b/backend/test/co-gestion.db.test.ts
@@ -0,0 +1,225 @@
+import type { FastifyInstance } from 'fastify'
+import { afterAll, beforeAll, beforeEach, describe, expect, it, vi } from 'vitest'
+
+// Co-gestion d'un arbre (#145), sur une vraie base : une fonction de droits se vérifie avec de vraies requêtes,
+// pas avec des mocks. Lancé seulement avec TEST_DATABASE_URL (base jetable, migrée) :
+//   TEST_DATABASE_URL=postgresql://postgres:postgres@localhost:5432/genealogy_test npx vitest run test/co-gestion.db.test.ts
+const TEST_DB = process.env.TEST_DATABASE_URL
+
+const { oidcMock } = vi.hoisted(() => ({ oidcMock: { startAuthorization: vi.fn(), finishAuthorization: vi.fn() } }))
+vi.mock('../src/lib/oidc.js', async (importOriginal) => ({
+  ...(await importOriginal<typeof import('../src/lib/oidc.js')>()),
+  ...oidcMock,
+}))
+
+const ISSUER = 'https://id.example.org'
+let app: FastifyInstance
+let env: { ALLOW_REGISTRATION: boolean; PASSWORD_LOGIN: boolean }
+let prisma: typeof import('../src/lib/prisma.js')['prisma']
+let ip = 0
+const nextIp = () => `10.1.${Math.floor(++ip / 250)}.${ip % 250 + 1}`
+const run = Date.now().toString(36)
+const mail = (name: string) => `${name}-${run}@exemple.fr`
+
+async function call(method: string, url: string, token?: string, payload?: unknown) {
+  const res = await app.inject({
+    method: method as 'GET',
+    url,
+    payload: payload as Record<string, unknown>,
+    headers: token ? { authorization: `Bearer ${token}` } : {},
+    remoteAddress: nextIp(),
+  })
+  return { status: res.statusCode, body: res.body ? res.json() : null }
+}
+
+async function register(name: string, extra: Record<string, unknown> = {}) {
+  const res = await call('POST', '/auth/register', undefined, { email: mail(name), password: 'mot-de-passe-solide', firstName: name, ...extra })
+  return res
+}
+
+async function account(name: string) {
+  const res = await register(name)
+  expect(res.status).toBe(201)
+  return { token: res.body.token as string, id: res.body.user.id as string, email: mail(name) }
+}
+
+describe.skipIf(!TEST_DB)('co-gestion, vraie base', () => {
+  let owner: { token: string; id: string; email: string }
+  let treeId: string
+
+  beforeAll(async () => {
+    process.env.NODE_ENV = 'test'
+    process.env.DATABASE_URL = TEST_DB
+    process.env.JWT_SECRET = 'test-secret-with-sufficient-length'
+    process.env.CORS_ORIGIN = 'http://localhost:5173'
+    process.env.OIDC_ISSUER = ISSUER
+    process.env.OIDC_CLIENT_ID = 'parenthese'
+    process.env.OIDC_CLIENT_SECRET = 'secret'
+    process.env.OIDC_REDIRECT_URI = 'https://arbre.example.org/auth/oidc/callback'
+    ;({ env } = await import('../src/config/env.js'))
+    ;({ prisma } = await import('../src/lib/prisma.js'))
+    const { createApp } = await import('../src/app.js')
+    app = createApp()
+    env.ALLOW_REGISTRATION = true
+    owner = await account('proprio')
+    const tree = await call('POST', '/trees', owner.token, { name: 'Arbre de démo', slug: `demo-${run}`, visitorPassword: 'partage-demo-1', contributorPassword: 'partage-demo-1' })
+    expect(tree.status).toBe(201)
+    treeId = tree.body.tree?.id ?? tree.body.id
+  })
+
+  beforeEach(() => {
+    env.ALLOW_REGISTRATION = true
+    env.PASSWORD_LOGIN = true
+  })
+
+  afterAll(async () => {
+    await app?.close()
+  })
+
+  async function invite(email: string) {
+    const res = await call('POST', `/trees/${treeId}/invitations`, owner.token, { email })
+    expect(res.status).toBe(201)
+    return res.body as { token: string; invitation: { id: string } }
+  }
+
+  it("un compte sans lien avec l'arbre ne voit ni ne change les gestionnaires", async () => {
+    const stranger = await account('inconnu')
+    expect((await call('GET', `/trees/${treeId}/managers`, stranger.token)).status).toBe(403)
+    expect((await call('POST', `/trees/${treeId}/invitations`, stranger.token, { email: stranger.email })).status).toBe(403)
+    expect((await call('DELETE', `/trees/${treeId}/managers/${owner.id}`, stranger.token)).status).toBe(403)
+    expect((await call('GET', `/trees/${treeId}/managers`)).status).toBe(401)
+  })
+
+  it("le lien n'ouvre rien au mauvais compte, ne sert qu'une fois, et donne les droits d'administration", async () => {
+    const coEmail = mail('cogest')
+    const { token, invitation } = await invite(coEmail)
+
+    const preview = await call('GET', `/invitations/${token}`)
+    expect(preview.status).toBe(200)
+    expect(preview.body.treeName).toBe('Arbre de démo')
+    expect(preview.body.emailHint).not.toContain(coEmail.split('@')[0])
+
+    // Le lien entre de mauvaises mains : un compte à une autre adresse ne l'accepte pas
+    const thief = await account('voleur')
+    expect((await call('POST', `/invitations/${token}/accept`, thief.token)).body.error).toBe('invitation_email_mismatch')
+    expect((await call('PATCH', `/trees/${treeId}`, thief.token, { name: 'Volé' })).status).toBe(403)
+
+    const co = await account('cogest')
+    const accepted = await call('POST', `/invitations/${token}/accept`, co.token)
+    expect(accepted.status).toBe(200)
+    expect(accepted.body).toEqual({ treeId, role: 'admin' })
+    expect((await call('POST', `/invitations/${token}/accept`, co.token)).status).toBe(404)
+    expect((await prisma.treeInvitation.findUnique({ where: { id: invitation.id } }))?.acceptedUserId).toBe(co.id)
+
+    // Co-gestionnaire : modifie l'arbre, voit la liste, mais n'invite pas, ne retire personne, ne supprime pas l'arbre
+    expect((await call('PATCH', `/trees/${treeId}`, co.token, { description: 'Par la co-gestionnaire' })).status).toBe(200)
+    const list = await call('GET', `/trees/${treeId}/managers`, co.token)
+    expect(list.body.canManage).toBe(false)
+    expect(list.body.managers.map((m: { role: string }) => m.role).sort()).toEqual(['admin', 'owner'])
+    expect((await call('POST', `/trees/${treeId}/invitations`, co.token, { email: mail('autre') })).status).toBe(403)
+    expect((await call('DELETE', `/trees/${treeId}/managers/${owner.id}`, co.token)).status).toBe(403)
+    expect((await call('DELETE', `/trees/${treeId}`, co.token, { confirmName: 'Arbre de démo' })).status).toBe(403)
+
+    // Le propriétaire le retire : son jeton de session ne sert plus à rien sur l'arbre, tout de suite
+    expect((await call('DELETE', `/trees/${treeId}/managers/${co.id}`, owner.token)).status).toBe(200)
+    expect((await call('PATCH', `/trees/${treeId}`, co.token, { description: 'Encore moi' })).status).toBe(403)
+    expect((await call('GET', `/trees/${treeId}/managers`, co.token)).status).toBe(403)
+  })
+
+  it('un co-gestionnaire quitte seul, et ne retire jamais un autre co-gestionnaire', async () => {
+    const a = await account('gestion-a')
+    const b = await account('gestion-b')
+    for (const who of [a, b]) {
+      const { token } = await invite(who.email)
+      expect((await call('POST', `/invitations/${token}/accept`, who.token)).status).toBe(200)
+    }
+    expect((await call('DELETE', `/trees/${treeId}/managers/${b.id}`, a.token)).status).toBe(403)
+    expect((await call('DELETE', `/trees/${treeId}/managers/${a.id}`, a.token)).status).toBe(200)
+    expect((await call('PATCH', `/trees/${treeId}`, a.token, { description: 'x' })).status).toBe(403)
+    expect((await call('PATCH', `/trees/${treeId}`, b.token, { description: 'y' })).status).toBe(200)
+    // Le propriétaire ne se retire pas lui-même
+    expect((await call('DELETE', `/trees/${treeId}/managers/${owner.id}`, owner.token)).status).toBe(403)
+    await call('DELETE', `/trees/${treeId}/managers/${b.id}`, owner.token)
+  })
+
+  it('« Copier le lien » remplace le lien ; annulé ou expiré, il ne sert plus', async () => {
+    const email = mail('rotation')
+    const first = await invite(email)
+    const rotated = await call('POST', `/trees/${treeId}/invitations/${first.invitation.id}/link`, owner.token)
+    expect(rotated.status).toBe(200)
+    expect((await call('GET', `/invitations/${first.token}`)).status).toBe(404)
+    expect((await call('GET', `/invitations/${rotated.body.token}`)).status).toBe(200)
+
+    expect((await call('DELETE', `/trees/${treeId}/invitations/${first.invitation.id}`, owner.token)).status).toBe(200)
+    const user = await account('rotation')
+    expect((await call('POST', `/invitations/${rotated.body.token}/accept`, user.token)).status).toBe(404)
+
+    const late = await invite(email)
+    await prisma.treeInvitation.update({ where: { id: late.invitation.id }, data: { expiresAt: new Date(Date.now() - 1000) } })
+    expect((await call('POST', `/invitations/${late.token}/accept`, user.token)).status).toBe(404)
+  })
+
+  it("inscription fermée : l'invitation ouvre un compte, à l'adresse invitée seulement", async () => {
+    const email = mail('ferme')
+    const { token } = await invite(email)
+    env.ALLOW_REGISTRATION = false
+
+    expect((await register('sans-invitation')).body.error).toBe('registration_closed')
+    expect((await register('autre-adresse', { invitationToken: token })).body.error).toBe('invitation_email_mismatch')
+    expect((await register('x', { invitationToken: 'faux-jeton' })).status).toBe(410)
+
+    const created = await register('ferme', { invitationToken: token })
+    expect(created.status).toBe(201)
+    expect(created.body.joinedTreeId).toBe(treeId)
+    expect((await call('PATCH', `/trees/${treeId}`, created.body.token, { description: 'z' })).status).toBe(200)
+    // Le lien a servi : il n'ouvre pas un second compte
+    expect((await call('POST', '/auth/register', undefined, { email: mail('ferme2'), password: 'mot-de-passe-solide', invitationToken: token })).status).toBe(410)
+    await call('DELETE', `/trees/${treeId}/managers/${created.body.user.id}`, owner.token)
+  })
+
+  describe('OIDC', () => {
+    let address = 0
+    async function oidcLogin(identity: { subject: string; email: string; emailVerified: boolean }) {
+      const remoteAddress = `10.9.0.${++address}`
+      oidcMock.startAuthorization.mockImplementation(async (returnTo: string) => ({
+        url: new URL(`${ISSUER}/authorize?state=s`),
+        pending: { state: 's', nonce: 'n', codeVerifier: 'v'.repeat(43), returnTo },
+      }))
+      oidcMock.finishAuthorization.mockResolvedValue({ issuer: ISSUER, firstName: null, ...identity })
+      const start = await app.inject({ method: 'GET', url: '/auth/oidc/start?returnTo=/', remoteAddress })
+      const cookie = String(start.headers['set-cookie']).split(';')[0]
+      const back = await app.inject({ method: 'GET', url: '/auth/oidc/callback?code=c&state=s', headers: { cookie }, remoteAddress })
+      return new URLSearchParams(String(back.headers.location).split('#')[1] ?? '')
+    }
+
+    it("email vérifié par le fournisseur : rattaché sans le lien, même inscription fermée", async () => {
+      const email = mail('oidc-ok')
+      await invite(email)
+      env.ALLOW_REGISTRATION = false
+      const fragment = await oidcLogin({ subject: `sub-ok-${run}`, email, emailVerified: true })
+      expect(fragment.get('oidc')).toBeTruthy()
+      const user = await prisma.user.findUnique({ where: { email }, select: { id: true } })
+      const membership = await prisma.treeMembership.findUnique({ where: { treeId_userId: { treeId, userId: user!.id } } })
+      expect(membership?.role).toBe('admin')
+    })
+
+    it("email non vérifié : jamais rattaché, et pas de compte sur une instance fermée", async () => {
+      const email = mail('oidc-non-verifie')
+      await invite(email)
+      env.ALLOW_REGISTRATION = false
+      const fragment = await oidcLogin({ subject: `sub-nv-${run}`, email, emailVerified: false })
+      expect(fragment.get('oidc_error')).toBe('oidc_email_unverified')
+      expect(await prisma.user.findUnique({ where: { email } })).toBeNull()
+    })
+
+    it("email non vérifié sur un compte déjà relié : l'invitation reste en attente", async () => {
+      const email = mail('oidc-relie')
+      const subject = `sub-relie-${run}`
+      expect((await oidcLogin({ subject, email, emailVerified: true })).get('oidc')).toBeTruthy()
+      await invite(email)
+      expect((await oidcLogin({ subject, email, emailVerified: false })).get('oidc')).toBeTruthy()
+      const user = await prisma.user.findUnique({ where: { email }, select: { id: true } })
+      expect(await prisma.treeMembership.findUnique({ where: { treeId_userId: { treeId, userId: user!.id } } })).toBeNull()
+    })
+  })
+})
diff --git a/backend/test/oidc.test.ts b/backend/test/oidc.test.ts
index ca4c795..9432191 100644
--- a/backend/test/oidc.test.ts
+++ b/backend/test/oidc.test.ts
@@ -15,6 +15,10 @@ const { prismaMock, oidcMock } = vi.hoisted(() => ({
       findUnique: vi.fn(),
       create: vi.fn(),
     },
+    treeInvitation: {
+      findFirst: vi.fn(),
+      findMany: vi.fn(),
+    },
     $transaction: vi.fn(),
     $executeRaw: vi.fn(),
     $disconnect: vi.fn(),
@@ -71,6 +75,8 @@ beforeEach(() => {
   prismaMock.user.count.mockResolvedValue(1)
   prismaMock.user.findUnique.mockResolvedValue(null)
   prismaMock.userIdentity.findUnique.mockResolvedValue(null)
+  prismaMock.treeInvitation.findFirst.mockResolvedValue(null)
+  prismaMock.treeInvitation.findMany.mockResolvedValue([])
   prismaMock.userIdentity.create.mockResolvedValue({})
   prismaMock.user.create.mockResolvedValue({ id: 'user-new' })
   prismaMock.$transaction.mockImplementation(async (run: (tx: typeof prismaMock) => unknown) => run(prismaMock))