User-friendliness is still not given enough importance in the design and development of e-commerce systems. This book examines the impact of user-friendly and well-designed e-shops on sales success. It begins with a discussion of the principles of usability and their implications for the design of e-shops. Following this, a framework for identifying success factors in e-commerce is developed, taking into account the methods of software and usability engineering as well as the principles of user-friendliness. The significance of user-friendliness for success in e-commerce is outlined, and recommendations for future developments of e-shops are provided.