Our contact with the world is through perception, and therefore the study of the process is of obvious importance and signi?cance. For much of its long history, the study of perception has been con?ned to natural- tic observation. Nonetheless, the phenomena considered worthy of note have not been those that nurture our survival-the veridical features of perception-but the oddities or departures from the common and c- monplace accuracies of perception. With the move from the natural world to the laboratory the oddities of perception multiplied, and they received ever more detailed scrutiny. My general intention is to examine the interpretations of the perc- tual process and its errors throughout history. The emphasis on errors of perception might appear to be a narrow approach, but in fact it enc- passes virtually all perceptual research from the ancients until the present. The constancies of perception have been taken for granted whereas - partures from constancies (errors or illusions) have fostered fascination.