Open textbooks are similar to traditional textbooks except that they are free of cost and licensed to allow revision and reuse. Adopting open textbooks for higher education courses is a way to address the growing costs of traditional textbooks that lead some students to be unable to access them, and to allow instructors to tailor the books to their own particular course context. Several empirical studies over the last few years have shown that open textbooks have the potential to increase student access to course readings without sacrificing quality. Adding to these results, this study focused on data from a new source: over fifty e-portfolios written by faculty about the use of open textbooks in their courses in several college and university systems in the state of California. We studied instructor's motivations for adopting an open textbook for their courses, the cost savings to students as a result of this adoption, the impact of assigning open textbooks on student learning outcomes and withdrawal rates, and other benefits and drawbacks of open textbooks. Faculty reported that cost savings was the most important motivation for adopting open textbooks, and that students most often reported this as what they appreciated about open textbooks. The vast majority of faculty also reported that the quality of the textbooks was as good or better than that of traditional textbooks, and that students did as well or better in terms of learning outcomes and withdrawal rates compared to when the same courses were run with traditional textbooks.