A Massive Open Online Course (MOOC) is a type of online learning environment that has the potential to increase students' access to education. However, the low completion rates in MOOCs suggest that student engagement and progression in the courses are problematic. Following the increasing adoption of gamification in education, it is possible that gamification can also be effectively adopted in MOOCs to enhance students' motivation and increase completion rates. Yet at present, the extent to which gamification has been examined in MOOCs is not known. Considering the myriad gamification elements that can be adopted in MOOCs (e.g., leaderboards and digital badges), this theoretical research study reviews scholarly publications examining gamification of MOOCs. The main purpose is to provide an overview of studies on gamification in MOOCs, types of research studies, theories applied, gamification elements implemented, methods of implementation, the overall impact of gamification in MOOCs, and the challenges faced by researchers and practitioners when implementing gamification in MOOCs. The results of the literature study indicate that research on gamification in MOOCs is in its early stages. While there are only a handful of empirical research studies, results of the experiments generally showed a positive relation between gamification and student motivation and engagement. It is concluded that there is a need for further studies using educational theories to account for the effects of employing gamification in MOOCs.