Iwas very grateful to be at the symposium and to make this contribution tothe volume celebrating the achievements of Bill Chase. Bill received hisMA at the University of Wisconsin and I was fortunate enough to serve as his major adviser. His MA was a remarkable contribution to the study of visual search and he pursued these issues for his PhD after I left Wisconsin to go to Oregon. It was typical of Bill’s high standards that little of this work was published at the time, although it did enter into several later papers. Bill was an empirical virtuoso capable of bringing high-level theory to test. When Bill moved to Carnegie Mellon, where Newell and Simon had done so much to bring theory to psychology, I felt strongly that important things would happen, and they did. Much of the most important work was in the ﬁeld of expertise, which we examine in this volume.