In previous columns I've explored reference e-book platforms, distributors, and aggregators. This month I want to step out a bit further and explore open-access digital textbooks. I learned a lot about digital textbooks in February when I attended the O'Reilly Tools of Change (TOC) Conference. This conference discusses issues in publishing; one of these issues happened to be digital textbooks. The first question that often comes to mind when discussing open-access digital textbooks is, what are they? They share several characteristics: they are protected by the creative commons license by which content may be copied, shared, or changed so long as the original author is attributed; they are developed by a community of authors or users and intended for educational purposes; and they are free.