diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7ad22c0..670d46a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,7 @@
 - Zoom feature
 - font selection
 - font size selection
+- line spacing button
 
 ### Not yet implemented
 - ODT import / open existing file
diff --git a/src/lib/editor/ToolbarExpanded.svelte b/src/lib/editor/ToolbarExpanded.svelte
index 30e2c5e..48b017d 100644
--- a/src/lib/editor/ToolbarExpanded.svelte
+++ b/src/lib/editor/ToolbarExpanded.svelte
@@ -75,8 +75,35 @@
     return mixed ? '' : (size ?? DEFAULT_FONT_SIZE);
   });
 
+  // Must match line-height in editor.css (.paper .tiptap)
+  const DEFAULT_LINE_HEIGHT = '1.5';
+  const LINE_HEIGHTS = [
+    { value: '1',    label: 'Single'      },
+    { value: '1.15', label: '1.15'        },
+    { value: '1.5',  label: '1.5'         },
+    { value: '2',    label: 'Double'      },
+  ] as const;
+
+  let currentLineHeight = $derived.by(() => {
+    if (tick < 0 || !editor) return DEFAULT_LINE_HEIGHT;
+    const { from, to, empty } = editor.state.selection;
+    if (empty) {
+      return editor.state.selection.$head.parent.attrs.lineHeight ?? DEFAULT_LINE_HEIGHT;
+    }
+    let lh: string | undefined;
+    let mixed = false;
+    editor.state.doc.nodesBetween(from, to, (node) => {
+      if (mixed || !('lineHeight' in node.attrs)) return;
+      const h: string = node.attrs.lineHeight ?? DEFAULT_LINE_HEIGHT;
+      if (lh === undefined) lh = h;
+      else if (lh !== h) mixed = true;
+    });
+    return mixed ? '' : (lh ?? DEFAULT_LINE_HEIGHT);
+  });
+
   let fontOpen = $state(false);
   let sizeOpen = $state(false);
+  let lineHeightOpen = $state(false);
   let sizeInputFocused = $state(false);
   let sizeInputValue = $state('');
   let savedFrom: number | null = null;
@@ -92,6 +119,7 @@
     if (!editor) return;
     sizeOpen = false;
     sizeInputFocused = false;
+    lineHeightOpen = false;
     // Save selection before the picker button steals focus.
     savedFrom = editor.state.selection.from;
     savedTo = editor.state.selection.to;
@@ -129,6 +157,7 @@
     if (!editor) return;
     sizeInputFocused = true;
     fontOpen = false;
+    lineHeightOpen = false;
     savedFrom = editor.state.selection.from;
     savedTo = editor.state.selection.to;
     (e.target as HTMLInputElement).select();
@@ -154,6 +183,7 @@
   function openSizePicker() {
     if (!editor) return;
     fontOpen = false;
+    lineHeightOpen = false;
     if (!sizeInputFocused) {
       savedFrom = editor.state.selection.from;
       savedTo = editor.state.selection.to;
@@ -177,6 +207,28 @@
     window.addEventListener('mousedown', handler);
     return { destroy() { window.removeEventListener('mousedown', handler); } };
   }
+
+  function openLineHeightPicker() {
+    if (!editor) return;
+    fontOpen = false;
+    sizeOpen = false;
+    sizeInputFocused = false;
+    lineHeightOpen = !lineHeightOpen;
+  }
+
+  function pickLineHeight(value: string) {
+    if (!editor) return;
+    lineHeightOpen = false;
+    editor.chain().focus().setLineHeight(value).run();
+  }
+
+  function lineHeightPickerClickOutside(node: HTMLElement) {
+    function handler(e: MouseEvent) {
+      if (!node.contains(e.target as Node)) lineHeightOpen = false;
+    }
+    window.addEventListener('mousedown', handler);
+    return { destroy() { window.removeEventListener('mousedown', handler); } };
+  }
 </script>
 
 <div class="toolbar-expanded">
@@ -254,6 +306,34 @@
 
     <div class="toolbar-separator"></div>
 
+    <div class="lh-picker" use:lineHeightPickerClickOutside>
+      <button class="lh-trigger" onclick={openLineHeightPicker} title="Line spacing">
+        <svg width="16" height="16" viewBox="0 0 16 16" fill="none" aria-hidden="true">
+          <line x1="5" y1="3"  x2="14" y2="3"  stroke="currentColor" stroke-width="1.5" stroke-linecap="round"/>
+          <line x1="5" y1="8"  x2="14" y2="8"  stroke="currentColor" stroke-width="1.5" stroke-linecap="round"/>
+          <line x1="5" y1="13" x2="14" y2="13" stroke="currentColor" stroke-width="1.5" stroke-linecap="round"/>
+          <path d="M2 5.5V1.5M2 1.5L1 2.8M2 1.5L3 2.8" stroke="currentColor" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"/>
+          <path d="M2 10.5V14.5M2 14.5L1 13.2M2 14.5L3 13.2" stroke="currentColor" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"/>
+        </svg>
+        <svg width="8" height="8" viewBox="0 0 8 8" fill="none" aria-hidden="true">
+          <path d="M1 2.5l3 3 3-3" stroke="currentColor" stroke-width="1.4" stroke-linecap="round" stroke-linejoin="round"/>
+        </svg>
+      </button>
+      {#if lineHeightOpen}
+        <div class="lh-dropdown">
+          {#each LINE_HEIGHTS as lh}
+            <button
+              class="lh-option"
+              class:active={currentLineHeight === lh.value}
+              onclick={() => pickLineHeight(lh.value)}
+            >{lh.label}</button>
+          {/each}
+        </div>
+      {/if}
+    </div>
+
+    <div class="toolbar-separator"></div>
+
     <div class="toolbar-group">
       <button
         class:active={isAlignLeft}
@@ -554,4 +634,70 @@
     background: var(--color-primary);
     color: white;
   }
+
+  .lh-picker {
+    position: relative;
+  }
+
+  .lh-trigger {
+    display: inline-flex;
+    align-items: center;
+    gap: 4px;
+    height: 2rem;
+    padding: 0 0.4rem;
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius);
+    background: var(--color-surface);
+    color: var(--color-text);
+    cursor: pointer;
+    min-width: unset;
+    transition: border-color 0.15s;
+  }
+
+  .lh-trigger:hover {
+    border-color: var(--color-primary);
+  }
+
+  .lh-dropdown {
+    position: absolute;
+    top: calc(100% + 3px);
+    left: 0;
+    min-width: 110px;
+    background: var(--color-surface);
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius);
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.12);
+    z-index: 200;
+    padding: 2px;
+    display: flex;
+    flex-direction: column;
+  }
+
+  .lh-option {
+    display: block;
+    width: 100%;
+    padding: 0.35rem 0.6rem;
+    border: none;
+    border-radius: calc(var(--radius) - 2px);
+    background: transparent;
+    color: var(--color-text);
+    font-size: 0.85rem;
+    font-family: var(--font-sans);
+    text-align: left;
+    cursor: pointer;
+    white-space: nowrap;
+    transition: background 0.1s;
+    min-width: unset;
+    height: auto;
+    justify-content: flex-start;
+  }
+
+  .lh-option:hover {
+    background: var(--color-btn-hover);
+  }
+
+  .lh-option.active {
+    background: var(--color-primary);
+    color: white;
+  }
 </style>
diff --git a/src/lib/editor/extensions.ts b/src/lib/editor/extensions.ts
index 3f64fd7..d952634 100644
--- a/src/lib/editor/extensions.ts
+++ b/src/lib/editor/extensions.ts
@@ -12,6 +12,7 @@ import ListItem from '@tiptap/extension-list-item';
 import History from '@tiptap/extension-history';
 import Placeholder from '@tiptap/extension-placeholder';
 import { PageBreaks } from './pageBreaks';
+import { LineHeight } from './lineHeight';
 
 export const extensions = [
   Document,
@@ -23,6 +24,7 @@ export const extensions = [
   TextStyle,
   FontFamily,
   FontSize,
+  LineHeight,
   Heading.configure({ levels: [1, 2, 3] }),
   BulletList,
   OrderedList,
diff --git a/src/lib/editor/lineHeight.ts b/src/lib/editor/lineHeight.ts
new file mode 100644
index 0000000..95bef54
--- /dev/null
+++ b/src/lib/editor/lineHeight.ts
@@ -0,0 +1,53 @@
+import { Extension } from '@tiptap/core';
+
+declare module '@tiptap/core' {
+  interface Commands<ReturnType> {
+    lineHeight: {
+      setLineHeight: (lineHeight: string) => ReturnType;
+      unsetLineHeight: () => ReturnType;
+    };
+  }
+}
+
+export const LineHeight = Extension.create({
+  name: 'lineHeight',
+
+  addOptions() {
+    return {
+      types: ['paragraph', 'heading'] as string[],
+    };
+  },
+
+  addGlobalAttributes() {
+    return [
+      {
+        types: this.options.types,
+        attributes: {
+          lineHeight: {
+            default: null,
+            parseHTML: (element: HTMLElement) => element.style.lineHeight || null,
+            renderHTML: (attributes: Record<string, unknown>) => {
+              if (!attributes.lineHeight) return {};
+              return { style: `line-height: ${attributes.lineHeight}` };
+            },
+          },
+        },
+      },
+    ];
+  },
+
+  addCommands() {
+    return {
+      setLineHeight: (lineHeight: string) => ({ commands }) => {
+        return this.options.types.every((type) =>
+          commands.updateAttributes(type, { lineHeight })
+        );
+      },
+      unsetLineHeight: () => ({ commands }) => {
+        return this.options.types.every((type) =>
+          commands.resetAttributes(type, 'lineHeight')
+        );
+      },
+    };
+  },
+});
diff --git a/src/lib/export/odt.ts b/src/lib/export/odt.ts
index 1c30fe5..ef5782e 100644
--- a/src/lib/export/odt.ts
+++ b/src/lib/export/odt.ts
@@ -1,14 +1,66 @@
 import type { Editor } from '@tiptap/core';
-import { tiptapToOdt } from 'odf-kit';
+import { tiptapToOdt, type TiptapNode, type TextFormatting, type OdtDocument, type ParagraphBuilder } from 'odf-kit';
+
+// tiptapToOdt ignores paragraph/heading node attrs (including lineHeight).
+// We rename nodes that carry lineHeight to custom types and handle them via
+// unknownNodeHandler, which has access to the full OdtDocument API.
+
+const LH_P = '__lh_p__';
+const LH_H = '__lh_h__';
+
+function injectLineHeightTypes(node: TiptapNode): TiptapNode {
+  if (node.attrs?.lineHeight) {
+    if (node.type === 'paragraph') return { ...node, type: LH_P };
+    if (node.type === 'heading')   return { ...node, type: LH_H };
+  }
+  if (node.content?.length) {
+    return { ...node, content: node.content.map(injectLineHeightTypes) };
+  }
+  return node;
+}
+
+function applyRuns(p: ParagraphBuilder, content: TiptapNode[] = []) {
+  for (const node of content) {
+    if (node.type !== 'text' || !node.text) continue;
+    const marks = node.marks ?? [];
+    const tsm = marks.find(m => m.type === 'textStyle');
+    const fmt: TextFormatting = {};
+    if (marks.some(m => m.type === 'bold'))      fmt.bold = true;
+    if (marks.some(m => m.type === 'italic'))     fmt.italic = true;
+    if (marks.some(m => m.type === 'underline'))  fmt.underline = true;
+    if (tsm?.attrs?.fontFamily) fmt.fontFamily = String(tsm.attrs.fontFamily);
+    if (tsm?.attrs?.fontSize)   fmt.fontSize   = String(tsm.attrs.fontSize);
+    if (tsm?.attrs?.color)      fmt.color      = String(tsm.attrs.color);
+    p.addText(node.text, Object.keys(fmt).length ? fmt : undefined);
+  }
+}
 
 export async function exportToOdt(editor: Editor): Promise<void> {
-  const json = editor.getJSON();
-  const odt = await tiptapToOdt(json);
+  const raw = editor.getJSON() as TiptapNode;
+  const json = injectLineHeightTypes(raw);
 
-  const blob = new Blob([odt], {
-    type: 'application/vnd.oasis.opendocument.text',
+  const odt = await tiptapToOdt(json, {
+    unknownNodeHandler(node: TiptapNode, doc: OdtDocument) {
+      const lhRaw = String(node.attrs?.lineHeight ?? '1.5');
+      const lhNum = parseFloat(lhRaw);
+      const lineHeight = isNaN(lhNum) ? lhRaw : lhNum;
+      const opts = { lineHeight };
+      const content = node.content ?? [];
+
+      if (node.type === LH_P) {
+        if (content.length === 0) {
+          doc.addParagraph('', opts);
+        } else {
+          doc.addParagraph((p: ParagraphBuilder) => applyRuns(p, content), opts);
+        }
+      } else if (node.type === LH_H) {
+        const level = (node.attrs?.level as number) ?? 1;
+        doc.addHeading((p: ParagraphBuilder) => applyRuns(p, content), level, opts);
+      }
+    },
   });
 
+  const blob = new Blob([odt as Uint8Array<ArrayBuffer>], { type: 'application/vnd.oasis.opendocument.text' });
   const url = URL.createObjectURL(blob);
   const a = document.createElement('a');
   a.href = url;
@@ -18,13 +70,14 @@ export async function exportToOdt(editor: Editor): Promise<void> {
 }
 
 function getFilename(editor: Editor): string {
-  // Try to derive filename from first heading
-  const json = editor.getJSON();
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const json = editor.getJSON() as any;
   const heading = json.content?.find(
-    (node) => node.type === 'heading' && node.content?.length
+    (node: any) => node.type === 'heading' && node.content?.length
   );
-  if (heading?.content?.[0]?.text) {
-    const name = heading.content[0].text
+  const firstText: string | undefined = heading?.content?.[0]?.text;
+  if (firstText) {
+    const name = firstText
       .slice(0, 50)
       .replace(/[^a-zA-Z0-9\s-]/g, '')
       .trim()
diff --git a/src/styles/editor.css b/src/styles/editor.css
index 61f6950..b27fe6f 100644
--- a/src/styles/editor.css
+++ b/src/styles/editor.css
@@ -24,7 +24,7 @@
   outline: none;
   font-family: var(--font-serif);
   font-size: 1.05rem;
-  line-height: 1.6;
+  line-height: 1.5;
   color: var(--color-text);
 
   /* Multi-page background: page surfaces separated by editor background */