The term “Fundamentalism” used as a comparative category within the academic study of religion has become problematic. Fundamentalism, is not one comprehensive movement but is, in fact, a phenomenon which encompasses a variety of beliefs, practices, and expectations. This thesis will explore the diversity of several different and distinct fundamentalist movements. I will discuss the natures of four Christian movements that have been labeled “fundamentalist” – Jehovah’s Witnesses, Christian Reconstructionists, Jerry Falwell and Pat Robertson – on several key points, eschatology, political philosophy, as well as level of social involvement. I will then turn to fundamentalism as it is used as a category to describe a global phenomenon. I will discuss three different scholarly approaches by turning to the work of Bruce Lawrence, Mark Juergensmeyer, and Bruce Lincoln on the Islamic “fundamentalist” group al- Qaeda. Finally I will argue that the category “fundamentalism” can be best understood in terms of a family resemblance.