This study investigates critical thinking (CT) studies in e-learning settings to provide a comprehensive analysis of CT studies. Research indexed in the Web of Science database which includes major peer-reviewed social sciences citation index journals in the e-learning field from January 2006 to November 2017 was searched for a systematic review and analysis. A total of 42 studies were selected and synthesized. The distribution of publishing years, geographical areas, education sectors, publications, disciplines, research methods, activities, CT measurement instruments, teaching instruction, the CT roles applied in the studies, and the experiment durations were reviewed. The results showed that most CT studies were conducted in nontraditional teaching environments using strategies such as online discussion or concept mapping; the most used quantitative method was the California critical thinking skills test (CCTST), whereas the most frequently adopted qualitative method was the practical inquiry model of cognitive presence (PIMCP). The common method to enhance students' CT was online synchronous or asynchronous discussion, and the role that CT played in these studies was as a dependent variable for evaluating whether the designed e-learning instruction(s) can cultivate CT. This study concludes that with active learning instruction and experienced tutor facilitation, students' CT could be enhanced in a variety of e-learning environments.