This text offers a user's guide to the philosophical work of Roy Bhaskar. The author expounds the main concepts of Bhaskar's work and defends his theory of knowledge. Part One deals with the philosophy of experimental science and discusses the stratification of nature, showing how biological structures are founded on chemical ones, yet are not reducible to them. Part Two discusses the human sciences, exploring Bhaskar's understanding of the human world and the ways in which it is studied in ethics, politics, economics, psychoanalysis and linguistics. His concept of an "explanatory critique" (an explanation that is also a criticism, not in addition to, but by virtue of, its explanatory work) is discussed at length as a key concept for ethics and politics. Collier concludes by looking at the uses to which critical realism has been put in clarifying disputes within the human sciences, with particular reference to linguistics, psychoanalysis, economics and politics.