Even acknowledging the considerable reservations of some users – we have to recognize the overall trend towards the use of e-books. The situation resembles the transition from print to electronic journals about ten years ago. Two trends are converging here: On the one hand, there is a strongly growing offer of scientific monographic literature in electronic format, and on the other hand, there has been significant progress in the technological possibilities for the reception of e-books, in particular regarding display technologies. The transition from print to electronic books provides a multiplicity of new challenges to the libraries, not least because of the overwhelming quantity of current and potential titles. For example, the ETH-Bibliothek has doubled the number of e-books in the catalogue in each year in the past few years. In 2008, for the first time more electronic than print monographs were purchased and catalogued. For the selection of e-books, the ETH-Bibliothek has defined extensive criteria. To include the individual titles of larger e-book packages into the catalogue, metadata were imported in a complex semi-automated procedure. There is only one catalogue record for printed and digital forms of the same title, so that users can immediately see, whether they can borrow the book in print form or access it directly online. A key feature for optimal benefits within the cataloguing network is the linking via a link resolver. For a stable compilation of the usage of electronic resources, the calculation of yearly usage on the basis of the median is described. Of course, many developments concerning the relatively new media type e-book are under way, and many questions are therefore still open. They range from acquisition models and the selection and processing of titles to possible restrictions on the use and the integration of freely available sources to the use of e-books in interlibrary loan and archiving.