This article reviews the core process of critical thinking--hunting assumptions--and explains how this process differs according to the context of what is being taught and the different intellectual traditions that inform teachers' own backgrounds. It outlines a basic protocol of critical thinking as a learning process that focuses on uncovering and checking assumptions, exploring alternative perspectives, and taking informed actions as a result. Three different categories of assumptions--paradigmatic, prescriptive, and causal--are defined, and the teaching methods and approaches that most help students to think critically are explored. The article examines in detail the fact that critical thinking is best experienced as a social learning process, and how important it is for teachers to model the process for students.