A recent development in wireless communications is the application of multiple-input multiple-output (MIMO) systems to radio communications via use of multiple antennas. In order to investigate the technology's potential, an experimental MIMO system which contains two four-element antenna arrays (4 × 4) has been developed at the University of Alberta. The system is used to obtain MIMO channel measurements in a typical indoor office environment in the ISM band (902 -928 MHz). Measurement campaigns were performed using different antenna spacings and two different types of antenna: half-wavelength (λ/2) centre-fed dipoles and dual polarized patches. The measurements are used to calculate channel capacities for an indoor 4 × 4 MIMO system. The measurements confirm the high capacity potential of a MIMO channel, with ergodic capacity of approximately 21 bits per channel use available with either antenna type at a signal-to-noise ratio of 20 dB if the antenna element separation is λ/2 or larger. An introduction to basic MIMO theory, a discussion of the University of Alberta wireless MIMO testbed, and observations regarding the measured indoor MIMO channel are presented in the paper.