The term “emerging adulthood” refers to individuals between the ages of 18 and 25 years and signifies a new time period of the life course in industrialized nations in which young adults have not fully taken on adult responsibilities but are also no longer teenagers. Emerging adulthood is the age period with the highest prevalence of drug use and drug abuse. The current paper addresses the question of why drug abuse is highest during this age period through a developmental approach that applies the distinctive features of emerging adulthood to the explanation of the prevalence of drug abuse. The author proposes that there are five developmentally distinctive features of emerging adulthood that explain why drug abuse is widespread during this age period: the age of identity explorations, the age of instability, the age of self-focus, the age of feeling in-between, and the age of possibilities. Each feature is explained in turn and 14 hypotheses relating to how these features of emerging adulthood increase the risk of drug abuse during this period are presented. The author urges future empirical testing of the hypotheses to contribute to a fuller understanding of the developmental basis of drug abuse during this period of the life phase. Figures, references