As is generally acknowledged, the work of Jan Willems on dissipativity has formed the foundation for large parts of systems and control theory as developed in the past fifty years. While working as an assistant professor in the Department of Electrical Engineering at MIT during the period between 1968 to 1973, he wrote the ground-breaking papers "Dissipative dynamical systems, General theory"; and "Dissipative dynamical systems, Linear systems with quadratic supply rates" in Archive for Rational Mechanics and Analysis [1], [2]. In these seminal papers he introduced the notion of a dissipative system. During the same period, he also made fundamental contributions to the subject of optimal control, in particular to linear quadratic problems with indefinite cost, and the associated algebraic Riccati equation [3]. Indeed, the most appealing framework for studying the Riccati equation is that of dissipative systems, because there the Riccati equation emerges in a natural way by reformulating the dissipation inequality (which expresses the fact that the system under consideration is dissipative) as a so-called linear matrix inequality (LMI). Together, [1], [2] and [3] are generally considered to provide the main concepts and analysis tools in many areas of linear and nonlinear systems and control, ranging from stability theory, linear quadratic optimal control and stochastic realization theory, to network synthesis, differential games and robust control.