As the demand for higher performance wireless communications continues to grow, novel algorithms have been developed which provide increased performance and efficiency. One such class of algorithms involves the use of multiple antennas on either end of a wireless link. Many of these multiple input multiple output (MIMO) algorithms offer impressive performance gains over their single antenna counterparts. The practicality of implementing such algorithms in a real system, however, has received far less attention. A primary reason for this is the scarcity of hardware platforms suitable for implementing and evaluating complex wireless communications algorithms. We present in this thesis two such platforms designed specifically to fill this void. The first platform is constructed from commercial off the shelf hardware, including equipment for baseband processing, RF up/downconversion and wireless channel emulation. The second, more ambitious platform, is built from custom hardware designed specifically for flexible MIMO prototyping.