Monitoring the Future (MTF) is a long-term study of American adolescents, college students, and adults through age 50. The study is supported under a series of investigator-initiated, competing research grants from the National Institute on Drug Abuse, and has been conducted annually by the University of Michigan's Institute for Social Research since 1975. The present volume is being published separately for the first time this year. Whereas the other three MTF monographs address the topic of substance use, the present volume focuses on a range of behaviors related to the spread of the human immunodeficiency virus (HIV) responsible for the acquired immunodeficiency syndrome (AIDS). The population under study is young adult high school graduates ages 21-30 in the general population. Previously, findings on this subject were presented as a final chapter in "Volume II" based on measures of HIV/AIDS risk and protective behaviors that were introduced into the MTF follow-up studies in 2004. However, as the content expanded considerably and the historical period lengthened, a separate volume on this important topic seemed warranted. (Contains 18 tables and 3 figures.) [For the related reports, see "Overview of Key Findings" (ED514371), 'Volume I" (ED514370), and "Volume II" (ED514367).]