This research analyzes motivations expressed by young, healthy, sedentary women before and after an exercise intervention. Young women (aged 18-30, n = 39) participated in focus groups or interviews during a 4-month exercise intervention. Afterward, 22 of these women and 20 controls completed physical activity diaries for 6 months and were interviewed. For the majority of women (n = 24), obligation to the study prevailed as the motivator during the intervention. Some ( n = 15) became physically active for their own benefit. Afterward, exercisers and controls said they were physically active to feel better and/or healthy (n = 20), for body image and/ or weight loss (n = 20), or both. Women expressed motivations for physical activity in ways that resonated with self-determination theory. Their commentaries expand on theory to include experiencing multiple motivations simultaneously and motivations shifting over time and in differing contexts. Social motivations were compelling, both those associated with societal values (research, health) and cultural trends (body image). (Contains 2 tables.)