The fourth year of medical school remains controversial, despite efforts to reform it. A committee from the Clerkship Directors in Internal Medicine and the Association of Program Directors in Internal Medicine examined transitions from medical school to internship with the goal of better academic advising for students. In 2013 and 2014, the committee examined published literature and the Web sites of 136 Liaison Committee on Medical Education-accredited schools for information on current course offerings for the fourth year of medical school. The authors summarized temporal trends and outcomes when available. Subinternships were required by 122 (90%) of the 136 schools and allow students to experience the intern's role. Capstone courses are increasingly used to fill curricular gaps. Revisiting basic sciences in fourth-year rotations helps to reinforce concepts from earlier years. Many schools require rotations in specific settings, like emergency departments, intensive care units, or ambulatory clinics. A growing number of schools require participation in research, including during the fourth year. Students traditionally take fourth-year clinical electives to improve skills, both within their chosen specialties and in other disciplines. Some students work with underserved populations or seek experiences that will be henceforth unavailable, whereas others use electives to "audition" at desired residency sites. Fourth-year requirements vary considerably among medical schools, reflecting different missions and varied student needs. Few objective outcomes data exist to guide students' choices. Nevertheless, both medical students and educators value the fourth year of medical school and feel it can fill diverse functions in preparing for residency.