Robinson's controversial introduction surveys this major topic in epistemology and philosophy of mind. The discussion covers perception theory from Descartes and the empiricists through Wittgenstein on privacy to contemporary physicalist theories. The focus, however, is on the sense-datum theory of perception. Robinson concludes that, despite attacks over the years, a modified version of this theory is essentially correct, overturning the consensus that has dominated the philosophy of perception for nearly half a century.