Patterned variation in commitment to fields of study by gender, race and social class persists in US higher education, reinforcing social stratification among those who receive college degrees. Yet how students and fields of study come together in college remains opaque, largely due to elective curriculums that oblige students to make numerous and iterative course selections as they move through academic time. This paper provides a framework for theorizing academic selection and guiding empirical work forward. We describe academic selection as a two-sided phenomenon, in which organizational processes provide courses offered and students select courses enrolled. Insights from social psychology, decision theory and organizational studies highlight complexity and contingency on both sides of academic selection. We argue that elective curriculums create garbage-can conditions in which commitments to fields of study consistently resist individual-level prediction, with implications for educational stratification and its legitimation in the United States.