As the editors of this excellent collection observe, much contemporary debate about perceptual experience is shaped by two lines of thought. Perception is in some sense ‘transparent’: it seems to put us in direct contact with the world. However, in non-standard experiences, such as illusions and hallucinations, how things appear is not a good guide to how they really are. One central set of issues concerns metaphysical questions about the right way to analyse the relation between experiences and the external physical objects we perceive, so as to make sense of both these features of perception. As the editors note in their useful introduction, traditional sense-datum theories of perception are now largely discredited. It is the rejection of sense-data that is largely responsible for the current support for the direct realist, or relational, view of perceptual experience, which several of the contributors uphold in one form or another. Yet there is a serious problem in providing a positive account of what the direct perception relation amounts to, if it is not to be explained in causal terms; no contemporary exponent of the relational view has so far succeeded in spelling out the precise nature of the relation that links the conscious experience of the subject and the particular physical object which is – supposedly – directly perceived. (There is an interesting parallel here: no sense-datum theorist was ever able to provide a satisfactory explanation of the acquaintance relation holding between the subject and a sense-datum.) Quite apart from this difficulty, the problems raised by the subjective similarity of veridical and non-standard cases of experience require some answers from the advocate of a non-causal account of perception.