Reliability of radio link is limited, owing to path loss, shadowing and multi-path fading. This necessitates the use of a certain type of diversity. In recent years, cooperative diversity has gained considerable attention.Here, wireless nodes cooperate in such a way that they share their antennas and other resources, to create a virtual array through distributed transmission and signal processing. This increases coverage and reduces transmitted power, thereby bringing down co-channel interference, which results in increased system capacity. This paper gives an overview of the state of art of various cooperation schemes and issues related to their implementation.