Questions about perception remain some of the most difficult and insoluble in both epistemology and in the philosophy of mind. This controversial but highly accessible introduction to the area explores the philosophical importance of those questions by re-examining what had until recent times been the most popular theory of perception - the sense-datum theory. Howard Robinson surveys the history of the arguments for and against the theory from Descartes to Husserl. He then shows that the objections to the theory, particularly Wittgenstein's attack on privacy and those of the physicalists, have been unsuccessful. He argues that we should return to the theory sense-data in order to understand perception. In doing so he seeks to overturn a consensus that has dominated the philosophy of perception for nearly half a century.