Antennas of transmitters and receivers have been manipulated to increase the capacity of transmission and reception of signals. Using many elements in antennas to shape beams and direct nulls in a particular point for optimum signal transmission and reception has over decades, had tremendous positive influence in received power and signal to noise ratio (SNR). However, since the antenna elements manipulation can be done both at base station and device terminal, it gives rise to an important method of using several antennas to put and obtain signals to and from space with increased capacity. This principle is termed Multiple-input and Multiple-output (MIMO). This paper discusses application of MIMO in the state of the art and next generation of wireless systems (5G). It also discusses four models of MIMO, SISO, SIMO, MISO and MIMO, considering three method of combing the signals from multipath propagations, Selection combining (SC), Equal gain combing (EGC) and maximum ratio combining (MRC). Spatial diversity and spatial multiplexing are also discussed as form of MIMO. Finally, Massive or Hyper MIMO which is a new method of increasing transmission capacity by very large scale for fifth generation of wireless system is discussed with its challenges and opportunities. Key terms-Diversity combining techniques, spatial multiplexing, channel state information (CSI). Massive MIMO