diff --git a/src/editor/contentState/index.js b/src/editor/contentState/index.js
index fbd8d02c..02999020 100644
--- a/src/editor/contentState/index.js
+++ b/src/editor/contentState/index.js
@@ -46,6 +46,7 @@ class ContentState {
   constructor (options) {
     const { eventCenter, bulletListMarker } = options
     Object.assign(this, options)
+
     // Use to cache the keys which you don't want to remove.
     this.exemption = new Set()
     this.blocks = [ this.createBlockP() ]
diff --git a/src/editor/contentState/tabCtrl.js b/src/editor/contentState/tabCtrl.js
index 42d5db1a..1ecfcb97 100644
--- a/src/editor/contentState/tabCtrl.js
+++ b/src/editor/contentState/tabCtrl.js
@@ -118,25 +118,27 @@ const tabCtrl = ContentState => {
     }
 
     this.appendChild(newList, listItem)
-    this.partialRender()
+    return this.partialRender()
   }
 
-  // ContentState.prototype.insertTab = function () {
-  //   // TODO(fxha): Tabs and all spaces with length > 1 are converted to a single space
-  //                  in editor mode. Maybe write a HTML "tab" element
-  //   // TODO(fxha): create setting entry "tabSize: <int>"
-  //   const tabCharacter = new Array(4).join(' ')
-  //   const { start, end } = this.cursor
-  //   const startBlock = this.getBlock(start.key)
-  //   const endBlock = this.getBlock(end.key)
-  //   if (this.cursor.start.key === this.cursor.end.key) {
-  //     startBlock.text = startBlock.text.substring(0, start.offset) + tabCharacter + endBlock.text.substring(end.offset)
-  //     // workaround: see todo 1
-  //     this.cursor.start.offset += 1 // tabCharacter.length
-  //     this.cursor.end.offset += 1 // tabCharacter.length
-  //     this.render()
-  //   }
-  // }
+  ContentState.prototype.insertTab = function () {
+    const tabSize = this.tabSize
+    const tabCharacter = ' '.repeat(tabSize)
+    const { start, end } = this.cursor
+    const startBlock = this.getBlock(start.key)
+    const endBlock = this.getBlock(end.key)
+    if (start.key === end.key && start.offset === end.offset) {
+      startBlock.text = startBlock.text.substring(0, start.offset) +
+        tabCharacter + endBlock.text.substring(end.offset)
+      const key = start.key
+      const offset = start.offset + tabCharacter.length
+      this.cursor = {
+        start: { key, offset },
+        end: { key, offset }
+      }
+      return this.partialRender()
+    }
+  }
 
   ContentState.prototype.tabHandler = function (event) {
     // disable tab focus
@@ -173,9 +175,8 @@ const tabCtrl = ContentState => {
 
     if (this.isIndentableListItem()) {
       return this.indentListItem()
-    } // else {
-    //   this.insertTab()
-    // }
+    }
+    return this.insertTab()
   }
 }
 
diff --git a/src/editor/index.js b/src/editor/index.js
index b9e93b34..4fb05512 100644
--- a/src/editor/index.js
+++ b/src/editor/index.js
@@ -21,7 +21,8 @@ class Aganippe {
   constructor (container, options) {
     const {
       focusMode = false, theme = 'light', markdown = '', preferLooseListItem = true,
-      autoPairBracket = true, autoPairMarkdownSyntax = true, autoPairQuote = true, bulletListMarker = '-'
+      autoPairBracket = true, autoPairMarkdownSyntax = true, autoPairQuote = true,
+      bulletListMarker = '-', tabSize = 4
     } = options
     this.container = container
     const eventCenter = this.eventCenter = new EventCenter()
@@ -35,7 +36,8 @@ class Aganippe {
       autoPairBracket,
       autoPairMarkdownSyntax,
       autoPairQuote,
-      bulletListMarker
+      bulletListMarker,
+      tabSize
     })
     this.emoji = new Emoji() // emoji instance: has search(text) clear() methods.
     this.focusMode = focusMode
@@ -539,6 +541,16 @@ class Aganippe {
     this.contentState.preferLooseListItem = preferLooseListItem
   }
 
+  setTabSize (tabSize) {
+    if (!tabSize || typeof tabSize !== 'number') {
+      tabSize = 4
+    } else if (tabSize < 1) {
+      tabSize = 1
+    }
+    this.tabSize = tabSize
+    this.contentState.tabSize = tabSize
+  }
+
   updateParagraph (type) {
     this.contentState.updateParagraph(type)
   }
diff --git a/src/renderer/components/editor.vue b/src/renderer/components/editor.vue
index 2fca3ef2..a39754ab 100644
--- a/src/renderer/components/editor.vue
+++ b/src/renderer/components/editor.vue
@@ -100,7 +100,7 @@
     },
     computed: {
       ...mapState([
-        'preferLooseListItem', 'autoPairBracket', 'autoPairMarkdownSyntax', 'autoPairQuote', 'bulletListItemMarker'
+        'preferLooseListItem', 'autoPairBracket', 'autoPairMarkdownSyntax', 'autoPairQuote', 'bulletListItemMarker', 'tabSize'
       ])
     },
     data () {
@@ -150,6 +150,12 @@
         if (value !== oldValue && editor) {
           editor.setListItemPreference(value)
         }
+      },
+      tabSize: function (value, oldValue) {
+        const { editor } = this
+        if (value !== oldValue && editor) {
+          editor.setTabSize(value)
+        }
       }
     },
     created () {
@@ -164,7 +170,8 @@
           autoPairBracket,
           autoPairMarkdownSyntax,
           autoPairQuote,
-          bulletListMarker
+          bulletListMarker,
+          tabSize
         } = this
 
         const { container } = this.editor = new Aganippe(ele, {
@@ -175,7 +182,8 @@
           autoPairBracket,
           autoPairMarkdownSyntax,
           autoPairQuote,
-          bulletListMarker
+          bulletListMarker,
+          tabSize
         })
 
         if (typewriter) {
diff --git a/src/renderer/store/editor.js b/src/renderer/store/editor.js
index 2eee14ce..369a335d 100644
--- a/src/renderer/store/editor.js
+++ b/src/renderer/store/editor.js
@@ -23,6 +23,7 @@ const state = {
   autoPairBracket: true,
   autoPairMarkdownSyntax: true,
   autoPairQuote: true,
+  tabSize: 4,
   // edit mode
   typewriter: false, // typewriter mode
   focus: false, // focus mode
diff --git a/static/preference.md b/static/preference.md
index bc9f1adf..7fcf6d4b 100755
--- a/static/preference.md
+++ b/static/preference.md
@@ -25,7 +25,8 @@ Edit and save to update preferences. You can only change the JSON below!
   "autoPairBracket": true,
   "autoPairMarkdownSyntax": true,
   "autoPairQuote": true,
-  "endOfLine": "default"
+  "endOfLine": "default",
+  "tabSize": 4
 }
 ```