The transition to adulthood has become a thriving area of research in life course studies. This review is organized around two of the field's emerging themes. The first theme is the increasing variability in pathways to adult roles through historical time. The second theme is a heightened sensitivity to transition behaviors as developmental processes. Accounts of such processes typically examine the active efforts of young people to shape their biographies or the socially structured opportunities and limitations that define pathways into adulthood. By joining these concepts, I suggest new lines of inquiry that focus on the interplay between agency and social structures in the shaping of lives.