It has become unimaginable to provide information – particularly scientific information – without e-books. They have become part of today’s combination of media, which includes printed books and journals, e-journals, e-books, and databases. When e-books first appeared on the market, librarians very quickly formulated their key requirements. The most important requirement is functionality: it must be possible to look through a book chapter by chapter, and also to get a quick overview of a comprehensive monograph. Usage arrangements, including concurrent usage and use for interlibrary loans, are also important. The use of uniform technical standards increases the acceptance of e-books.