This chapter presents a state of the art of the congestion control protocols in vehicular ad hoc networks (VANET). A tendency toward decentralized congestion control is emerging at the level of academic research, as well as at the level of standardization, more particularly within the European Telecommunications Standards Institute (ETSI) where several technical specifications have been published on this subject. Five approaches are discussed in the chapter: the first approach based on the adaptation of the sending frequency of beacons, the second approach based on the increase in data transmission flow rate, the third approach based on the transmission power control in order to increase the channel capacity, the fourth approach based on the reduction of the contention window size and, finally, the fifth approach based on carrier sensing. A performance assessment of several adaptive mechanisms involved is presented by comparing them to the IEEE 802.11p standard mechanism.