Advanced communication scenarios demand the development of new systemswhere antenna theory, channel propagation and communication models are seen from a common perspective as a way to understand and optimize the system as a whole. In this context, a comprehensive multiantenna formulation for multiple-input multiple-output systems is presented with a special emphasis on the connection of the electromagnetic and communication principles. Starting from the capacity for amultiantenna system, the book reviews radiation, propagation, and communicationmechanisms, paying particular attention to the vectorial, directional, and timefrequency characteristics of the wireless communication equation for low- and high-scattering environments. Based on the previous concepts, different spacetime methods for diversity and multiplexing applications are discussed, multiantenna modeling is studied, and specific tools are introduced to analyze the antenna coupling mechanisms and formulate appropriate decorrelation techniques.Miniaturization techniques for closely spaced antennas are studied, and its fundamental limits and optimization strategies are reviewed. Finally, different practical multiantenna topologies for new communication applications are presented, and its main parameters discussed. A relevant feature is a collection of synthesis exercises that review the main topics of the book and introduces state-of-the art system architectures and parameters, facilitating its use either as a text book or as a support tool for multiantenna systems design.