This volume is a direct result of a conference held at Princeton University to honor George A. Miller, an extraordinary psychologist. A distinguished panel of speakers from various disciplines -- psychology, philosophy, neuroscience and artificial intelligence -- were challenged to respond to Dr. Miller's query: "What has happened to cognition? In other words, what has the past 30 years contributed to our understanding of the mind? Do we really know anything that wasn't already clear to William James?" Each participant tried to stand back a little from his or her most recent work, but to address the general question from his or her particular standpoint. The chapters in the present volume derive from that occasion.