Mobile ad hoc network is established to overcome the limitation of wired networks and infrastructure based wireless networks. Architecture of mobile ad hoc network is very much different from its counterparts. Many issues and challenges are present in mobile ad hoc networks. Link breakage is most frequent due to nodes movement which is the main reason of route failure in MANET. Due to this, transmission of data in ad hoc environment exhibit less network performance. Nodes are self-organizing. These nodes may move freely and change their position dynamically. Congestion control is one of the most challenging task in MANET. Different techniques have been proposed to control congestion in this paper we give an overview over existing methods. The purpose of this paper is to discuss and compare different congestion control techniques.