The rise of mobile platforms and the Web has created a market where software is now funded by advertisements, subscriptions and in-app purchases. This software is designed with retention in mind, motivating users to return to the application again and again.

However, developers struggle to understand exactly how to motivate users. This lack of understanding has given rise to the easy answers of 'gamification' and 'social', without providing the foundational psychological knowledge developers need to truly understand their users' needs. New frameworks are required to bridge this knowledge gap.

This dissertation presents one such framework, a library of twenty-seven motivational design patterns, under the categories of gameful, social, interface and information. Theories and experimental results from motivational psychology, behavioral psychology and behavioral economics are used to explain the power of diferent design patterns and suggest optimal implementations. Additionally, a set of eight dark patterns are presented. These patterns promise the developer short-term gains, but at the expense of long-term motivational harm, and strategies to avoid their use are proposed.

To validate the applicability of the pattern library, it is used in case studies that analyze existing software designs, and generate new ones from problem statements. The existence of the pattern library not only brings us greater understanding about how motivational software works, but provides us with a language with which to communicate motivational design, and a framework to begin the work on improving software's ability to meet users' motivational needs.