The GTAS MIMO Testbed is an open access wireless network hardware demonstrator developed in the GTAS group at the University of Cantabria and conceived for the practical evaluation of multiuser multiantenna transmission techniques. The testbed consists of three transmit/receive nodes each equipped with Multiple Input Multiple Output (MIMO) capabilities. The testbed is suitable for assessing the performance of different transmission methods over wireless network channels, such as multiple access channels, broadcast channels, relay channels or interference channels. Obviously, it is also useful to evaluate transmission methods for point-to-point channels.