Colleges are not the only enterprises interested in the possibilities of free, online courses. Publishers have begun to investigate whether so-called MOOC's, or massive open online courses, can help them reach new readers and sell more books. For the moment, providers of the classes encourage professors not to require students to buy texts, in order to keep access as open as possible. So publishers cannot count on MOOCs to generate a course-adoption sales. But online courses do have recommended-reading lists, and enrollments in the tens of thousands. The courses' recommended-reading lists represent "a promising market for university-press titles," says the director of one press. Online courses have another advantage: They attract many international students, a group that university presses are trying harder to reach.