This is the 20th year that the Minnesota Symposium on Child Psychology has provided the opportunity to take stock of an important area in the field. It is especially fitting that this anniversary should be combined with a symposium designed to honor the memory of a prominent contributor to the chosen area, and this symposium on perceptual development, in honoring Philip Salapatek, does just that. It is also fitting that the area, perceptual development, is ripe for stock taking. The last 20 years have witnessed an impressive accumulation of exciting discoveries in the area. It has gained more than an accumulation of new facts; it has so broadened and differentiated that new questions, new methods, and new concepts are rife. The time has come to consider the undoubted progress and search for ways of ordering and organizing the flood of information that we now possess.