ADDPLAN Adaptive Designs - Plans and Analyses was first released in 2002. Since then, interest in performing clinical trials with flexible (adaptive) designs has been permanently growing. The availability of a reliable, comprehensive, user-friendly and professionally validated statistical planning and analysis software package has never been so important before. We developed ADDPLAN along these lines and the new Release 4 was considerably enhanced and improved. Many recent developments in statistical theory were considered in the development process. As before, ADDPLAN lays special emphasis on adaptive group sequential test designs but also offers a much broader range of applicability.