Abstract: I discuss how online postsecondary education, including massive open online courses (MOOCs), might fit into economically sustainable models of postsecondary education. I contrast nonselective postsecondary education (NSPE) in which institutions sell fairly standardized educational services in return for up- front payments and highly selective postsecondary education (HSPE) in which institutions invest in students in return for repayments much later in life. The analysis suggests that MOOCs will be financially sustainable substitutes for some NSPE but that MOOCs will be financially sustainable substitutes for only a small share of HSPE. I discuss non-MOOC models of online education that may allow HSPE institutions both to sustain their distinctive activities and to reach a larger number of students.