During the past two decades, there has been a dramatic increase in interest in the study of aging-related changes in cognitive abilities. In this volume researchers from a variety of theoretical perspectives discuss adult age differences in a wide range of cognitive skills. Of special interest is the extent to which aging effects on performance are related to variations in the representation, organization, and utilization of knowledge, broadly defined. Recent research and theory in the field of aging has emphasized the need to examine such processes more closely in order to provide a more complete understanding of aging effects on cognitive behavior.