The objective of this book is to provide information that will be useful to people in a variety of disciplines who wish to learn more about normal aging processes in the human body. Although gerontologists in the biological sciences are making great strides in research on human aging and documenting this work in monographs, texts, and review chapters, this information is generally not easily acces­ sible nor is it comprehensible to nonprofessionals in these fields. This book is intended to provide a summary of this work, along with its implications for psy­ chological functioning of the aging individual. The majority of the book is devoted to describing the results of research on the physiological changes in the human body with aging and to seeking explanations for these age effects. This description has been approached in such a way as to make it readable for the nonspecialist, but also to focus on research issues that will be useful reading for those who are currently working in these parti­ cular areas. In addition, throughout the book, I have tried to develop some themes regarding physiological and psychological adaptation during adulthood.