Historically, health science education has focused on content knowledge. However, there has been increasing recognition that education must focus more on the thinking processes required of future health professionals. In an effort to teach these processes, educators of health science students have looked to the concept of critical thinking. But what does it mean to “think critically”? Despite some attempts to clarify and define critical thinking in health science education and in other fields, it remains a “complex and controversial notion that is difficult to define and, consequently, difficult to study” (Abrami et al., 2008, p. 1103). This selected review offers a roadmap of the various understandings of critical thinking currently in circulation. We will survey three prevalent traditions from which critical thinking theory emerges and the major features of the discourses associated with them: critical thinking as a set of technical skills, as a humanistic mode of accessing creativity and exploring self, and as a mode of ideology critique with a goal of emancipation. The goal of this literature review is to explore the various ways in which critical thinking is understood in the literature, how and from where those understandings emerge, and the debates that shape each understanding.