diff --git a/app/assets/stylesheets/request-for-comments.css.scss b/app/assets/stylesheets/request-for-comments.css.scss
index cbaf9d36..6448e6e7 100644
--- a/app/assets/stylesheets/request-for-comments.css.scss
+++ b/app/assets/stylesheets/request-for-comments.css.scss
@@ -17,3 +17,50 @@
   width: 100%;
   height: 200px;
 }
+
+.ace_tooltip {
+  display: none !important;
+}
+
+p.comment {
+  width: 400px;
+}
+
+.popover-header {
+  width: 100%;
+  overflow: hidden;
+  padding-bottom: 10px;
+  margin: auto;
+}
+
+.popover-username {
+  font-weight: bold;
+  width: 60%;
+  float: left;
+}
+
+.popover-date {
+  text-align: right;
+  color: #008cba;
+  margin-left: 60%;
+  font-size: x-small;
+}
+
+.popover-updated {
+  text-align: right;
+  margin-left: 60%;
+  font-size: x-small;
+}
+
+.popover-comment {
+  word-wrap: break-word;
+  margin-bottom: 10px;
+}
+
+.popover-divider {
+  width: 100%;
+  height: 1px;
+  background-color: #008cba;
+  overflow: hidden;
+  margin-bottom: 10px;
+}
diff --git a/app/controllers/comments_controller.rb b/app/controllers/comments_controller.rb
index f6e4f7fb..01dcd9d5 100644
--- a/app/controllers/comments_controller.rb
+++ b/app/controllers/comments_controller.rb
@@ -19,6 +19,8 @@ class CommentsController < ApplicationController
       @comments = Comment.where(file_id: params[:file_id])
       @comments.map{|comment|
         comment.username = comment.user.displayname
+        comment.date = comment.created_at.strftime('%d.%m.%Y %k:%M')
+        comment.updated = (comment.created_at != comment.updated_at)
       }
     else
       @comments = []
diff --git a/app/models/comment.rb b/app/models/comment.rb
index ceeb9c36..a5946ac9 100644
--- a/app/models/comment.rb
+++ b/app/models/comment.rb
@@ -1,7 +1,7 @@
 class Comment < ActiveRecord::Base
   # inherit the creation module: encapsulates that this is a polymorphic user, offers some aliases and makes sure that all necessary attributes are set.
   include Creation
-  attr_accessor :username
+  attr_accessor :username, :date, :updated
 
   belongs_to :file, class_name: 'CodeOcean::File'
   belongs_to :user, polymorphic: true
diff --git a/app/policies/comment_policy.rb b/app/policies/comment_policy.rb
index ef7a0922..549c8438 100644
--- a/app/policies/comment_policy.rb
+++ b/app/policies/comment_policy.rb
@@ -12,7 +12,7 @@ class CommentPolicy < ApplicationPolicy
     everyone
   end
 
-  [:new?, :destroy?].each do |action|
+  [:new?, :destroy?, :update?].each do |action|
     define_method(action) { admin? || author? }
   end
 
diff --git a/app/views/comments/index.json.jbuilder b/app/views/comments/index.json.jbuilder
index 85172014..55dfac49 100644
--- a/app/views/comments/index.json.jbuilder
+++ b/app/views/comments/index.json.jbuilder
@@ -1,4 +1,4 @@
 json.array!(@comments) do |comment|
-  json.extract! comment, :id, :user_id, :file_id, :row, :column, :text, :username
+  json.extract! comment, :id, :user_id, :file_id, :row, :column, :text, :username, :date, :updated
   json.url comment_url(comment, format: :json)
 end
diff --git a/app/views/request_for_comments/show.html.erb b/app/views/request_for_comments/show.html.erb
index 6a21ca24..ab60ef91 100644
--- a/app/views/request_for_comments/show.html.erb
+++ b/app/views/request_for_comments/show.html.erb
@@ -64,6 +64,8 @@
   </h5>
 </div>
 <hr>
+
+<div class="hidden sanitizer"></div>
 <!--
 do not put a carriage return in the line below. it will be present in the presentation of the source code, otherwise.
 also, all settings from the rails model needed for the editor configuration in the JavaScript are attached to the editor as data attributes here.
@@ -140,6 +142,18 @@ also, all settings from the rails model needed for the editor configuration in t
     currentEditor.on("guttermousedown", handleSidebarClick);
   });
 
+  function cleanupPopovers() {
+    // remove all possible popovers
+    $('.editor > .ace_gutter > .ace_gutter-layer > .ace_gutter-cell').popover('destroy');
+  }
+
+  function preprocess(commentText) {
+      // sanitize comments to deal with XSS attacks:
+      commentText = $('div.sanitizer').text(commentText).html();
+      // display original line breaks:
+      return commentText.replace(/\n/g, '<br>');
+  }
+
   function setAnnotations(editor, fileid) {
     var session = editor.getSession();
 
@@ -153,18 +167,65 @@ also, all settings from the rails model needed for the editor configuration in t
     });
 
     jqrequest.done(function(response){
-      $.each(response, function(index, comment) {
-        comment.className = "code-ocean_comment";
+      // comments need to be sorted to cluster them per line
+      var comments = response.slice().sort(function (a, b) {
+          return a.row - b.row;
+      });
+      while (comments.length > 0) {
+        // new cluster of comments
+        var cluster = [];
+        var clusterRow = comments[0].row;
+        // now collect all comments on this line
+        while (comments.length > 0 && comments[0].row === clusterRow) {
+          cluster.push(comments.shift());
+        }
+        // sort the comments by creation date
+        cluster = cluster.sort(function (a, b) {
+            return a.id - b.id;
+        });
 
+        // build the markup for the current line's popover
+        var popupContent = '';
+        cluster.forEach(function(comment, index) {
+            if (index !== 0) {
+                popupContent += '<div class="popover-divider"></div>'
+            }
+            popupContent += '<p class="comment">';
+            popupContent += '<div class="popover-header">' +
+                '<div class="popover-username">' + preprocess(comment.username) + '</div>' +
+                '<div class="popover-date">' + comment.date + '</div>';
+            if (comment.updated) {
+                popupContent += '<div class="popover-updated">' +
+                    '<i class="fa fa-pencil" aria-hidden="true"></i>' +
+                    '<%= t('request_for_comments.comment_edited') %>' +
+                    '</div>'
+            }
+            popupContent += '</div>';
+            popupContent += '<div class="popover-comment">' + preprocess(comment.text) + '</div>';
+            popupContent += '</p>';
+        });
+
+        // attach the popover to the ace sidebar (where the comment icon is displayed)
+        var icon = $('*[data-file-id="' + fileid + '"]')          // the editor for this file
+                .find('.ace_gutter > .ace_gutter-layer')          // the sidebar
+                .find('div:nth-child(' + (clusterRow + 1) + ')'); // the correct line
+        icon.popover({
+          content: popupContent,
+          html: true, // necessary to style comments. XSS is not possible due to comment pre-processing (sanitizing)
+          trigger: 'hover',
+          container: 'body'
+        });
+      }
+
+      $.each(response, function(index, comment) {
+        comment.className = 'code-ocean_comment';
         // if we have tabs or carriage returns in the comment, just add the name and leave it as it is. otherwise: format!
         if(comment.text.includes("\n") || comment.text.includes("\t")){
           comment.text = comment.username + ": " + comment.text;
         } else {
           comment.text = comment.username + ": " + stringDivider(comment.text, 80, "\n");
         }
-
       });
-
       session.setAnnotations(response);
     })
   }
@@ -182,6 +243,7 @@ also, all settings from the rails model needed for the editor configuration in t
   }
 
   function deleteComment(file_id, row, editor) {
+    cleanupPopovers();
     var jqxhr = $.ajax({
       type: 'DELETE',
       url: "/comments",
@@ -196,6 +258,7 @@ also, all settings from the rails model needed for the editor configuration in t
   }
 
   function createComment(file_id, row, editor, commenttext){
+    cleanupPopovers();
     var jqxhr = $.ajax({
       data: {
         comment: {
diff --git a/config/locales/de.yml b/config/locales/de.yml
index 021f65a7..090b1823 100644
--- a/config/locales/de.yml
+++ b/config/locales/de.yml
@@ -466,6 +466,7 @@ de:
     write_a_thank_you_node: "Wenn Sie möchten, können Sie sich bei allen Mitstudenten, die Ihnen bei der Beantwortung Ihrer Frage geholfen haben, bedanken:"
     send_thank_you_note: "Senden"
     cancel_thank_you_note: "Nichts senden"
+    comment_edited: "bearbeitet"
   sessions:
     create:
       failure: Fehlerhafte E-Mail oder Passwort.
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 9a334697..1d7ed507 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -487,6 +487,7 @@ en:
     write_a_thank_you_node: "If you want, you can write a thank you note to all your commenters:"
     send_thank_you_note: "Send"
     cancel_thank_you_note: "Don't send"
+    comment_edited: "edited"
   sessions:
     create:
       failure: Invalid email or password.