The present volume presents new 2017 findings from the U.S. national Monitoring the Future (MTF) follow-up study concerning substance use among the nation's college students and adults from ages 19 through 55. The authors report 2017 prevalence estimates on numerous illicit and licit substances, examine how substance use differs across this age span, and show how substance use and related behaviors and attitudes have changed over the past four decades. MTF, now in its 44th 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 integrated MTF 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 authors report the results of the repeated cross-sectional surveys of all high school graduating classes since 1976 as they follow them into their adult years (as discussed in Chapter 3, these cross-sections come from longitudinal data). 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), to whom we refer as the "young adult" sample; and (4) high school graduates at the specific later modal ages of 35, 40, 45, 50, and 55. This volume emphasizes historical and developmental changes in substance use and related attitudes and beliefs occurring at these age strata. 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 2017 follow-up surveys of the graduating high school classes of 1976 through 2016, as these respondents have progressed into adulthood. The oldest MTF respondents, from the classes of 1976-80, have been surveyed through age 55 in 2013-2017, 37 years after their graduation. [For the report from the previous year "Monitoring the Future National Survey Results on Drug Use, 1975-2016. Volume II, College Students & Adults Ages 19-55," see ED578605. For Volume I "Monitoring the Future National Survey Results on Drug Use, 1975-2017. Volume I, Secondary School Students," see ED589763. For "Demographic Subgroup Trends among Adolescents in the Use of Various Licit and Illicit Drugs, 1975-2017. Monitoring the Future Occasional Paper Series. Paper 90," see ED589759. For "Monitoring the Future National Survey Results on Drug Use, 1975-2017: Overview, Key Findings on Adolescent Drug Use," see ED589762.]