The growing interest in professional development for teachers via massive open online courses (MOOCs) raises the need for identifying the existing gaps in the literature on the topic. In this literature review, we were able to identify 68 relevant studies. They mostly used mixed methods (57%) and surveys (82%), and only reported descriptive statistics (52%). They also tended to measure participants' attitudes (41%) and engagement (40%). Based on our findings, we recommend that future researchers consider additional data collection and analysis methods (e.g., clickstream data, objective performance measures) and use correlational, longitudinal, and experimental designs.