H-infinity control theory is a subject that deals with the minimization of the H-infinity norm of the transfer matrix from an exogenous disturbance to a pertinent controlled output of a given plant. This is an examination of both the theoretical and practical aspects of H-infinity control from the angle of the structural properties of linear systems. Constructive algorithms for finding solutions to general singular H-infinity control problems are presented, as well as solutions to general H-infinity almost disturbance recoupling problems, and the applications of the theory to real-life problems with actual implementations is also presented. It deals with all such issues for general continuous- and discrete-time systems.