"Karl Popper is one of the greatest and most influential philosophers of the twentieth century. Perhaps his greatest book, The Logic of Scientific Discovery, sets out his epistemology of critical rationalism, while his most famous book, The Open Society and Its Enemies, applies the principles of critical rationalism to social philosophy." This book is more comprehensive than any current introduction to Popper. Owing to its perspicuous structure and lucid exposition, it could be used in courses in both the philosophy of science and the philosophy of social science.