Goal-setting theory has been used for decades to explain how to motivate people to perform better in work-related tasks, but more recently gamification has also gained attention as an alternative method to increase engagement and performance in many contexts. However, despite goals and feedback being common elements of gameful implementations, there is a lack of literature explaining how gamification works through the lens of goal-setting theory or suggesting how goal-setting concepts and recommendations can be employed to improve gameful systems. Therefore, we present a literature review and a conceptual framework that establishes a relationship between goal-setting and gamification concepts. Next, we describe how this framework can help explain gamification principles and suggest potential improvements to current gameful design methods. Finally, we propose directions for future empirical research aimed to apply this conceptual framework in practice.