The growing miniaturization of electronic devices combined with the recent developments in wearable computer technology have been leading to the creation of a wide range of devices which can be carried in a pocket or attached to a user's body. These applications have allowed the removal of the need for wired interconnections and have led to the rise of the concept of the wireless body area network (WBAN). These networks have a wide range of applications such as healthcare, smart home, monitoring, mobile entertainment, etc. To ensure the efficient performance of such wireless networks the radio propagation channels and the antenna systems need to be characterized and modeled. This study focuses on the characterization of the channel of WBANs and on the design of a body worn antenna. To face the fading generated by the body movement, a MIMO antenna has been designed exploiting the Theory of the Characteristic Modes. This research covers several topics and should be especially useful to professionals in Communication Technologies or anyone else who wants to increase knowledge in on body wireless networks and MIMO multimode antennas.