Why do some young adults substantially change their patterns of smoking, drinking, or illicit drug use after graduating from high school? In this book, the authors show that leaving high school and leaving home create new freedoms that are linked to increases in the use of cigarettes, alcohol, marijuana, and cocaine. They also show that marriage, pregnancy, and parenthood create new responsibilities that are linked to decreases in drug use. The research is based on more than 33,000 young people followed from high school through young adulthood by the nationwide Monitoring the Future project. Every two years, participants reported on their drug use, as well as their schooling, employment, military service, living arrangements, marriages, pregnancies, parenthood, and even their divorces. The unique qualities of this research--large nationally representative samples, follow-ups extending up to 14 years beyond high school, and multiple approaches to analysis and data presentation--allowed the examination of several important influences simultaneously, while retaining much of the rich detail encountered in the real world. On the whole, the results are encouraging, suggesting that the potentials for change and improvement during the transition to adulthood are as important as the detrimental effects of problem behavior in adolescence. This research is a must read for anyone concerned with how new freedoms and responsibilities impact adolescents, young adults, and the use of licit and illicit drugs.