In the nearly two decades since the HIV pandemic began, the rapid expansion of behavioral research on HIV prevention has prompted a crucial need for a sourcebook more advanced than an introductory textbook and broader and more readily accessible than a review periodical. The Handbook of HIV Prevention is intended as the first attempt to meet this need. The current state of affairs led us to edit a book that would represent the major areas of HIV behavioral research at a level appropriate for graduate students and experienced researchers in public health, medicine, nursing, education, and the social and behavioral sciences. In addition, we expect that the handbook will be useful in advanced undergraduate courses and as a reference book for health care professionals. Our plans to assemble the Handbook began in the fall of 1996 when we prepared a tentative outline of chapters and invited a large number of distinguished researchers in the field to be the authors of various chapters. We received an overwhelmingly favorable response from potential authors to our letters of invitation. After considerable effort by both the contributors and the editors the volume was completed in 1999, when all chapters went to press.