The article starts with an overview of the current knowledge on the transition to adulthood and a short discussion of the evolution of the age composition of the university student population in a Canadian province. [...] Liefbroer (1999) provides a list of such factors, grouped in two categories: changes in the economic and social structure (the expansion of the educational system, the increase in the labour force participation of women, economic development, the creation and revision of the welfare state, and changes in the economic structure) and cultural factors (the decrease in the normative controls of behavi [...] The composition of the postsecondary student population The evolution of the age composition of the university student population in Quebec—one of the ten Canadian provinces— is a good way to illustrate the interaction between the transition to adulthood and the postsecondary student population. [...] Overall, the evolution of the number of students aged 24 or less is driven by 10 the size of their cohorts in the population and by the increase of the proportion of youth that attends university. [...] Interest in the composition of the student population is more likely to arise from the postsecondary system as a social system—or from people studying it as a social system: changes in the age composition of the student population, and thus of the psychic systems it interacts with, may force the social system to change the role it assigns to students and may even alter the goal of the system.