Born in Austria, Karl Popper (1902-1994) was one of the dominant philosophical thinkers of the 20th century. A ground-breaking thinker, he saw the essence of true science as being the readiness to submit theories to severe testing and to reject them when refuted by test. His first major book in 1935, The Logic of Scientific Discovery, marked him as a major analyst of science and was to have an enormous influence on the way people, including major scientists, came to think about the field. Popper contrasted his philosophy of science against Marxists and psychoanalysts such as Freud and Adler, who piled up 'confirmations' of their theories, but took no notice of refutations. He was scandalized by the way Marxists and other left-wing agitators were prepared to use human lives in order to achieve long-term (and dubious) political goals. His two major contributions to political philosophy The Open Society and its Enemies and The Poverty of Historicism have had an abiding influence throughout the world, and led to the description of Popper on his obituaries as 'The Man who Destroyed Marx and Freud'. Philosophy of science remained central to Popper, but his explanation of how knowledge grew in science was extended into a general theory of problem solving in all areas and also into a more general theory of rationality. Popper was a tireless campaigner against relativism and irrationality. He asserted the reality and value of individual freedom, and the unpredictability of history, very much against the spirit of his age (mid-1940s). In all these areas, he made major philosophical contributions, the implications of which are still being worked out and discussed. This collection is a timely assessment of the reactions to and abiding influence of Popper's work, and controversy it caused across many academic and political fields. The set includes early responses to Popper's work from sources difficult to obtain, and also two early reviews (by Carnap and Grelling) in translations specially prepared for this set. It is organised thematically, and includes a substantial new introduction by the editor in the first volume.