diff --git a/public/src/modules/helpers.js b/public/src/modules/helpers.js
index 838ad7a4da..bc40bde658 100644
--- a/public/src/modules/helpers.js
+++ b/public/src/modules/helpers.js
@@ -26,7 +26,7 @@
 		if (groupObj.isMember) {
 			return '<button class="btn btn-danger" data-action="leave" data-group="' + groupObj.name + '"><i class="fa fa-times"></i> Leave Group</button>';
 		} else {
-			if (groupObj.pending) {
+			if (groupObj.isPending) {
 				return '<button class="btn btn-warning disabled"><i class="fa fa-clock-o"></i> Invitation Pending</button>';
 			} else {
 				return '<button class="btn btn-success" data-action="join" data-group="' + groupObj.name + '"><i class="fa fa-plus"></i> Join Group</button>';
diff --git a/src/groups.js b/src/groups.js
index 60019a47b9..eadabda28f 100644
--- a/src/groups.js
+++ b/src/groups.js
@@ -144,6 +144,14 @@ var async = require('async'),
 					next(null, isMember);
 				});
 			},
+			isPending: function(next) {
+				// Retrieve group membership state, if uid is passed in
+				if (!options.uid) {
+					return next();
+				}
+
+				db.isSetMember('group:' + groupName + ':pending', options.uid, next);
+			},
 			isOwner: function(next) {
 				// Retrieve group ownership state, if uid is passed in
 				if (!options.uid) {
@@ -173,12 +181,19 @@ var async = require('async'),
 			results.base.deletable = !results.base.system;
 			results.base.truncated = truncated;
 			results.base.isMember = results.isMember;
+			results.base.isPending = results.isPending;
 			results.base.isOwner = results.isOwner;
 
 			callback(err, results.base);
 		});
 	};
 
+	Groups.isPrivate = function(groupName, callback) {
+		db.getObjectField('group:' + groupName, 'private', function(err, isPrivate) {
+			callback(err, isPrivate || isPrivate === null);	// Private, if not set at all
+		});
+	};
+
 	Groups.getMembers = function(groupName, callback) {
 		db.getSetMembers('group:' + groupName + ':members', callback);
 	};
@@ -521,6 +536,20 @@ var async = require('async'),
 		});
 	};
 
+	Groups.requestMembership = function(groupName, uid, callback) {
+		db.setAdd('group:' + groupName + ':pending', uid, callback);
+		plugins.fireHook('action:groups.requestMembership', {
+			groupName: groupName,
+			uid: uid
+		});
+	};
+
+	Groups.approveMembership = function(groupName, uid, callback) {
+		// Note: For simplicity, this method intentially doesn't check the caller uid for ownership!
+		db.setRemove('group:' + groupName + ':pending', uid, callback);
+		Groups.join.apply(Groups, arguments);
+	};
+
 	Groups.leave = function(groupName, uid, callback) {
 		callback = callback || function() {};
 
diff --git a/src/socket.io/groups.js b/src/socket.io/groups.js
index 943b9dc10c..366a12348f 100644
--- a/src/socket.io/groups.js
+++ b/src/socket.io/groups.js
@@ -1,6 +1,7 @@
 "use strict";
 
 var	groups = require('../groups'),
+	meta = require('../meta'),
 
 	SocketGroups = {};
 
@@ -9,7 +10,17 @@ SocketGroups.join = function(socket, data, callback) {
 		return callback(new Error('[[error:invalid-data]]'));
 	}
 
-	groups.join(data.groupName, socket.uid, callback);
+	if (meta.config.allowPrivateGroups) {
+		groups.isPrivate(data.groupName, function(err, isPrivate) {
+			if (isPrivate) {
+				groups.requestMembership(data.groupName, socket.uid, callback);
+			} else {
+				groups.join(data.groupName, socket.uid, callback);
+			}
+		});
+	} else {
+		groups.join(data.groupName, socket.uid, callback);
+	}
 };
 
 SocketGroups.leave = function(socket, data, callback) {