Electronic textbooks, often lauded as a cheaper alternative to hard copies, may also seem like a perfect way for colleges to reduce their greenhouse-gas emissions. Many institutions encourage use of e-books, and one state, California, has required that all textbooks used in college classes be made available electronically by 2020. In a sign of growing campus interest in cutting carbon emissions, nearly 700 institutions have signed the American College & University Presidents' Climate Commitment, pledging to reduce their footprint and to promote education and research on climate change. On the surface, this transition to digital media makes perfect sense: After all, purchased materials of all kinds make up a quarter of most colleges' carbon footprints, and textbooks (in hard-copy form) represent about a quarter of emissions from purchased materials. However, the reality is not so simple. E-textbooks require electricity to operate, and if students print out many pages from them, the resulting carbon footprint may actually be greater than that of the hard-copy textbooks they are replacing. With so much uncertainty, the authors set out to answer the question: Which is more climate friendly--hard-copy textbooks or e-textbooks? They compared the greenhouse-gas emissions of both throughout their life cycles, including creation, distribution, student usage, and disposal, using existing emissions-related data and the results of a survey they conducted of 200 students in six undergraduate classes. They discovered that when they consider all greenhouse-gas emissions over the life cycle of the textbook, from raw-material production to disposal or reuse, the differences between the two types of textbooks are actually quite small. More importantly, they discovered that the ways that hard-copy and digital textbooks are used have a huge effect on emissions. Colleges that are serious about reducing their carbon footprint, then, should realize that the behavior of students, faculty members, and administrators plays a crucial role. Faculty members and administrators should consider educating students on how to print more efficiently, either through classroom instructions or more comprehensive campus-awareness campaigns. They should make sure students understand that opting for an e-textbook and then printing a huge number of pages from it is environmentally unfriendly. Faculty members should also recognize that forcing students who prefer the printed page to buy e-textbooks is unwise. The answer to the question of which is best, then, is that it depends on the behavior of students--and that is something that faculty members and administrators can strongly influence.