Questions about perception remain some of the most difficult and insoluble in both epistemology and in the philosophy of mind. This controversial but 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 discusses the empiricist conception of sense-contents and examines the traditional arguments for sense-data and objections to the theory, particularly Wittgenstein's attack on privacy and the current physicalist approaches to perception. He constructs and defends a strengthened version of the causal argument for sense-data, and argues that appeals to intentionality and adverbialism are unsuccessful. He also shows that representative realism and, more particularly, phenomenalism can circumvent most of the traditional objections to the theory, and contends that we should return to the theory sense-data in order to understand perception.