Multiple-Input-Multiple-Output systems (MIMO) are regarded as one of the most promising research areas of wireless communication systems In wireless communication, elevated data broadcast rates are essential for the needs i.e. data, voice & video. At user end the capacity resolves the excellence of the communication systems. Transmission techniques of MIMO are two types one is diversity gain and second one is multiplexing gain. Fading mitigation and transmitted signal performance can be improved by diversity gain. Under prosperous dispersion environment multiplexing gain offers the high broadcast rates. Cooperative relaying is a expertise technology that can improve the performance of a wireless system via a number of mechanisms, such as increased spatial diversity. In this paper, a review of the prominent results like improving the user throughput and cell average throughput using relays in Cooperative – Multiple –Input-Multiple- Output systems (CMIMO).