diff --git a/Jakefile.js b/Jakefile.js
index 4340aa5e..e4546709 100644
--- a/Jakefile.js
+++ b/Jakefile.js
@@ -38,7 +38,7 @@ task('build', {async: true}, function () {
     src: [
       './src/timeline/component/css/timeline.css',
       './src/timeline/component/css/panel.css',
-      './src/timeline/component/css/groupset.css',
+      './src/timeline/component/css/labelset.css',
       './src/timeline/component/css/itemset.css',
       './src/timeline/component/css/item.css',
       './src/timeline/component/css/timeaxis.css',
diff --git a/src/timeline/component/Group.js b/src/timeline/component/Group.js
index 408cad52..c22ce385 100644
--- a/src/timeline/component/Group.js
+++ b/src/timeline/component/Group.js
@@ -1,14 +1,22 @@
 /**
  * @constructor Group
  * @param {Number | String} groupId
+ * @param {Object} data
  * @param {ItemSet} itemSet
  */
-function Group (groupId, itemSet) {
+function Group (groupId, data, itemSet) {
   this.groupId = groupId;
 
   this.itemSet = itemSet;
 
   this.dom = {};
+  this.props = {
+    label: {
+      width: 0,
+      height: 0
+    }
+  };
+
   this.items = {};        // items filtered by groupId of this group
   this.visibleItems = []; // items currently visible in window
   this.orderedItems = {   // items sorted by start and by end
@@ -17,6 +25,8 @@ function Group (groupId, itemSet) {
   };
 
   this._create();
+
+  this.setData(data);
 }
 
 /**
@@ -43,6 +53,30 @@ Group.prototype._create = function() {
   this.dom.axis = document.createElement('div');
 };
 
+/**
+ * Set the group data for this group
+ * @param {Object} data   Group data, can contain properties content and className
+ */
+Group.prototype.setData = function setData(data) {
+  // update contents
+  var content = data && data.content;
+  if (content instanceof Element) {
+    this.dom.inner.appendChild(content);
+  }
+  else if (content != undefined) {
+    this.dom.inner.innerHTML = content;
+  }
+  else {
+    this.dom.inner.innerHTML = this.groupId;
+  }
+
+  // update className
+  var className = data && data.className;
+  if (className) {
+    util.addClassName(this.dom.label, className);
+  }
+};
+
 /**
  * Get the foreground container element
  * @return {HTMLElement} foreground
@@ -67,6 +101,15 @@ Group.prototype.getAxis = function getAxis() {
   return this.dom.axis;
 };
 
+/**
+ * Get the width of the group label
+ * @return {number} width
+ */
+Group.prototype.getLabelWidth = function getLabelWidth() {
+  return this.props.label.width;
+};
+
+
 /**
  * Repaint this group
  * @param {{start: number, end: number}} range
@@ -75,6 +118,8 @@ Group.prototype.getAxis = function getAxis() {
  * @return {boolean} Returns true if the group is resized
  */
 Group.prototype.repaint = function repaint(range, margin, restack) {
+  var resized;
+
   if (typeof margin === 'number') {
     margin = {
       item: margin,
@@ -94,8 +139,6 @@ Group.prototype.repaint = function repaint(range, margin, restack) {
 
   // recalculate the height of the group
   var height;
-
-  // determine the height from the stacked items
   var visibleItems = this.visibleItems;
   if (visibleItems.length) {
     var min = visibleItems[0].top;
@@ -109,8 +152,7 @@ Group.prototype.repaint = function repaint(range, margin, restack) {
   else {
     height = margin.axis + margin.item;
   }
-
-  var resized = (this.height != height);
+  resized = (this.height != height);
 
   // calculate actual size and position
   var foreground = this.dom.foreground;
@@ -119,8 +161,14 @@ Group.prototype.repaint = function repaint(range, margin, restack) {
   this.width = foreground.offsetWidth;
   this.height = height;
 
+  // recalculate size of label
+  // TODO: if changed, return resized=true
+  this.props.label.width = this.dom.inner.clientWidth;
+  this.props.label.height = this.dom.inner.clientHeight;
+
   // apply new height
   foreground.style.height  = height + 'px';
+  this.dom.label.style.height = height + 'px';
 
   return resized;
 };
diff --git a/src/timeline/component/ItemSet.js b/src/timeline/component/ItemSet.js
index a9f2445a..a92fff7d 100644
--- a/src/timeline/component/ItemSet.js
+++ b/src/timeline/component/ItemSet.js
@@ -8,26 +8,21 @@ var UNGROUPED = '__ungrouped__'; // reserved group id for ungrouped items
  *                                vertical lines of box items.
  * @param {Panel} axisPanel       Panel on the axis where the dots of box-items
  *                                can be displayed.
- * @param {Panel} labelPanel      Left side panel holding labels
+ * @param {Panel} sidePanel      Left side panel holding labels
  * @param {Object} [options]      See ItemSet.setOptions for the available options.
  * @constructor ItemSet
  * @extends Panel
  */
-function ItemSet(backgroundPanel, axisPanel, labelPanel, options) {
+function ItemSet(backgroundPanel, axisPanel, sidePanel, options) {
   this.id = util.randomUUID();
 
   // one options object is shared by this itemset and all its items
   this.options = options || {};
   this.backgroundPanel = backgroundPanel;
   this.axisPanel = axisPanel;
-  this.labelPanel = labelPanel;
+  this.sidePanel = sidePanel;
   this.itemOptions = Object.create(this.options);
   this.dom = {};
-  this.props = {
-    labels: {
-      width: 0
-    }
-  };
   this.hammer = null;
 
   var me = this;
@@ -110,6 +105,12 @@ ItemSet.prototype._create = function _create(){
   this.dom.axis = axis;
   this.axisPanel.frame.appendChild(axis);
 
+  // create labelset
+  var labelSet = document.createElement('div');
+  labelSet.className = 'labelset';
+  this.dom.labelSet = labelSet;
+  this.sidePanel.frame.appendChild(labelSet);
+
   // create ungrouped Group
   this._updateUngrouped();
 
@@ -166,6 +167,11 @@ ItemSet.prototype.hide = function hide() {
   if (this.dom.background.parentNode) {
     this.dom.background.parentNode.removeChild(this.dom.background);
   }
+
+  // remove the labelset containing all group labels
+  if (this.dom.labelSet.parentNode) {
+    this.dom.labelSet.parentNode.removeChild(this.dom.labelSet);
+  }
 };
 
 /**
@@ -182,6 +188,11 @@ ItemSet.prototype.show = function show() {
   if (!this.dom.background.parentNode) {
     this.backgroundPanel.frame.appendChild(this.dom.background);
   }
+
+  // show labelset containing labels
+  if (!this.dom.labelSet.parentNode) {
+    this.sidePanel.frame.appendChild(this.dom.labelSet);
+  }
 };
 
 /**
@@ -338,7 +349,8 @@ ItemSet.prototype._updateUngrouped = function _updateUngrouped() {
     // create a group holding all (unfiltered) items
     if (!ungrouped) {
       var id = null;
-      ungrouped = new Group(id, this, this.dom.background, this.dom.axis, this.labelPanel.frame);
+      var data = null;
+      ungrouped = new Group(id, data, this);
       this.groups[UNGROUPED] = ungrouped;
 
       for (var itemId in this.items) {
@@ -381,7 +393,7 @@ ItemSet.prototype.getAxis = function getAxis() {
  * @return {HTMLElement} labelSet
  */
 ItemSet.prototype.getLabelSet = function getLabelSet() {
-  return this.labelPanel.frame;
+  return this.dom.labelSet;
 };
 
 /**
@@ -631,7 +643,8 @@ ItemSet.prototype._onAddGroups = function _onAddGroups(ids) {
         height: null
       });
 
-      group = new Group(id, me, me.dom.background, me.dom.axis, me.labelPanel.frame);
+      var data = me.groupsData.get(id);
+      group = new Group(id, data, me);
       me.groups[id] = group;
 
       // add items with this groupId to the new group
@@ -763,7 +776,13 @@ ItemSet.prototype._constructByEndArray = function _constructByEndArray(array) {
  * @return {Number} width
  */
 ItemSet.prototype.getLabelsWidth = function getLabelsWidth() {
-  return this.props.labels.width;
+  var width = 0;
+
+  util.forEach(this.groups, function (group) {
+    width = Math.max(width, group.getLabelWidth());
+  });
+
+  return width;
 };
 
 /**
diff --git a/src/timeline/component/css/itemset.css b/src/timeline/component/css/itemset.css
index 7b75428d..0864aedf 100644
--- a/src/timeline/component/css/itemset.css
+++ b/src/timeline/component/css/itemset.css
@@ -25,6 +25,7 @@
 
 .vis.timeline  .group {
   position: relative;
+  box-sizing: border-box;
 }
 
 .vis.timeline.top .group {
diff --git a/src/timeline/component/css/groupset.css b/src/timeline/component/css/labelset.css
similarity index 76%
rename from src/timeline/component/css/groupset.css
rename to src/timeline/component/css/labelset.css
index cbc501b9..0daa809f 100644
--- a/src/timeline/component/css/groupset.css
+++ b/src/timeline/component/css/labelset.css
@@ -20,14 +20,12 @@
   box-sizing: border-box;
 }
 
-.vis.timeline.bottom .labelset .vlabel,
-.vis.timeline.top .vpanel.side-content {
+.vis.timeline.top .labelset .vlabel {
   border-top: 1px solid #bfbfbf;
   border-bottom: none;
 }
 
-.vis.timeline.top .labelset .vlabel,
-.vis.timeline.bottom .vpanel.side-content {
+.vis.timeline.bottom .labelset .vlabel {
   border-top: none;
   border-bottom: 1px solid #bfbfbf;
 }