The problem of asymptotic regulation of the output of a dynamical system plays a central role in control theory. An important variant of this problem is the output regulation problem, which can be used in areas such as s- point control, tracking reference signals and rejecting disturbances generated by an external system, controlled synchronization of dynamical systems, and observer design for autonomous systems. At the moment this is a hot topic in nonlinear control. This book is a result of a four-year research project conducted at the Eindhoven University of Technology. This project, entitled “Robust output regulation for complex dynamical systems,� began with the observation that theproblemofcontrolledsynchronizationofdynamicalsystemscanbecons- ered as a particular case of the output regulation problem. In the beginning of the project, known solutions to the controlled synchronization problem were global and dealt with nonlinear systems having complex (“chaotic�) dyn- ics. At the same time, most of the existing solutions to the nonlinear output regulation problem were local and dealt mostly with exosystems being linear harmonicoscillators. Ourinitialideawas,usingtheresultsfromthecontrolled synchronization problem as a starting point, to extend solutions of the n- linear output regulation problem from the local case to the global case and to avoid restrictive assumptions on the exosystem. As a ?rst step, we started looking for points that were common to these two problems.