<P> <B> </B> This book provides a comprehensive, step-by-step treatment of the state-space <I>H</I>?à control theory, reflecting recent theoretical developments this area, in particular, and in the area of robust and <I>H</I>? à control theory in general. It offers as self-contained a presentation as possible and, for reference sake, includes many background results on linear systems, the theory and application of Riccati equations and model reduction. </P>