Thanks to the features of the mobile devices which have been constantly evolving, there has been a diversity of mobile applications. It is highly possible to find a mobile application to carry out any transaction in an application store. Users, whose expectations have been increasing, hope that libraries will be accessible and controllable. Hence, libraries should move towards mobile platforms so that users can easily get access to them. In this study, we first review the criteria that should be paid attention when designing mobile applications for iPhone and then describe the iPhone mobile application that we developed for Hacettepe University Libraries.