Teaching students to use critical thinking skills is a popular goal of many economics courses. But what does "critical thinking" really mean, and how is it implemented? This article considers various interpretations of "critical thinking" and distinguishes "big-think" from "little-think" critical thinking, arguing that both are necessary. Teaching little-think critical thought involves teaching the tools, models, and methods that economists use in understanding some aspect of economics, while teaching big-think critical thought involves teaching textbook economic models' applicability to the real world and how value judgments are integrated with scientific evidence to reach supportable policy positions. The authors argue that, while there is no one right way to teach principles, instructors should consider the tradeoffs and include both dimensions of critical thinking in their courses.