MIMO OFDM communications is a promising choice for future high data rate wireless systems. However, the commercial deployment of MIMO OFDM systems faces some challenges, including those arising from front-end analog implementation impairments and complex receiver structures. The impairments are caused by the analog processing of the received radio frequency (RF) signal and they cannot be efficiently nor entirely eliminated in the analog domain. This paper illustrates the effect of In-phase and Quadrature-phase (IQ) imbalances on system performance. Receiver algorithms are described that compensate for IQ imbalances. The structure of space-time block codes, along with the assumed structure of the distortion models, are exploited to design reduced-complexity adaptive receivers that are robust to IQ imbalances.