The Henri Poincaré Prize 1997 was awarded to Rudolf Haag for his fundamental contributions to the quantum theory of systems with infinitely many degrees of freedom, as one of the founders of modern Quantum Field Theory, where he discovered the central role of the principle of locality and of the concept of local observables as roots of all the conceptual and formal structures; and as a leader in the operator algebraic analysis of the foundations of Quantum Statistical Mechanics. Of all these aspects his recent book is a superb condensation.