Monitoring the Future (MTF), now in its 41st year, is a research program conducted at the University of Michigan's Institute for Social Research under a series of investigator-initiated, competing research grants from the National Institute on Drug Abuse--one of the National Institutes of Health. The study comprises several ongoing series of annual surveys of nationally representative samples of 8th- and 10th-grade students (begun in 1991), 12th-grade students (begun in 1975), and high school graduates followed into adulthood (begun in 1976). The current monograph reports the results of the repeated cross-sectional surveys of all high school graduating classes since 1976 as researchers followed them into their adult years. Segments of the general adult population represented in these follow-up surveys include: (1) U.S. college students; (2) their age-peers who are not attending college, sometimes called the "forgotten half"; (3) all young adult high school graduates of modal ages 19 to 30 (or 19-28 for trend estimates), referred to as the "young adult" sample; and (4) high school graduates at the specific later modal ages of 35, 40, 45, 50, and 55. In this volume, historical and developmental changes in substance use and related attitudes and beliefs occurring at these age strata receive particular emphasis. The follow-up surveys have been conducted by mail on representative subsamples of the previous participants from each high school senior class. This volume presents data from the 1977 through 2015 follow-up surveys of the graduating high school classes of 1976 through 2014, as these respondents have progressed into adulthood. The oldest MTF respondents, from the class of 1976, were the first to be surveyed through age 55 in 2013--37 years after their graduation. An index is included. [For "Monitoring the Future National Survey Results on Drug Use, 1975-2015. Volume 1, Secondary School Students," see ED578604.]