In a letter of 1932, Karl Popper described Die Beiden Grundrpobleme der Erkenntnistheorie - 'The Two Fundamental Problems of Knowledge' - as "...a child of crises, ... above all of ... the crisis of physics. It asserts the permanence of crisis; if it is right, then crisis is the normal state of a highly developed rational science." Finally available in English for the first time, it is a major contribution to the philosophy of science and twentieth century philosophy generally. Drawing on important research Popper carried out between 1930 and 1933, Die Beiden Grundrpobleme der Erkenntnistheorie was not published in German until the early 1980's. The two fundamental problems of knowledge that lie at the center of the book are the problems of induction, the theory that although we are only able to observe a limited number of particular events, science nevertheless advances universal statements; and the problem of demarcation; what separates empirical science from non-science? Popper seeks to solve these two basic problems with his celebrated theory of falsificationism. He argues that science is separated from non-science not by the verifiability but by the falsifiability of its theories. Popper also argues that science is not inductive but ultimately deductive; it does not start out from observations and generalize from them, as many presumed, but starts with problems, which it attacks with bold conjectures. As such, The Two Fundamental Problems of Knowledge contains many of the celebrated arguments that were to later find full expression in Popper's most celebrated work, The Logic of Scientific Discovery. It is therefore essential reading for anyone interested in Karl Popper, the history and philosophy of science ,and the methods and theories of science itself.