Space-time wireless technology that uses multiple antennas along with appropriate signaling and receiver techniques offers a powerful tool for improving wireless performance. Multiple antennas when used with appropriate Space-Time Block Coding (STBC) techniques can achieve huge performance gains in multipath fading wireless links. MIMO systems with multiple antenna elements at both transmitter and receiver ends are an efficient solution for future wireless communications systems. This paper describes Multiple-Input Multiple-Output (MIMO) systems using Alamouti based space-time block coding technique at the transmitter and Maximal Ratio Combining (MRC) at the receiver.