The courses and majors college students select are important determinants of academic progress, timely degree completion, and future career paths. Yet academic selection is a complicated phenomenon under elective curriculums, in which students confront serial occasions for selecting multiple courses and majors as they move through academic time. This complexity is potentially fateful for postsecondary trajectories, yet researchers only recently have obtained the computational tools to observe and model it at scale. This paper reviews prior work on course and major selection, notes its assets and limitations, and provides a conceptual framework for theorizing, observing, and modeling academic selection under the conditions of curricular complexity, iterative selection, organizational anarchy, and goal ambiguity that characterize elective curriculums. A cumulative science in this domain can inform development of selection architectures that improve transparency and equity in academic selection, progress and degree completion.