Fundamentalism is a term that originated in the United States. Early in the 20th century, Protestant groups adopted the designation to differentiate themselves from forms of liberal Protestantism and secularists (Jones, 2010). The recent coinage of fundamentalism suggests that its development is related to modernity, and while fundamentalist movements are characterized by their commitment to traditional belief-systems, they are often highly innovative adaptations to the modern experience. In this paper, the relationship between fundamentalism and modernity will be analysed; first by elaborating the concept of modernity and then reviewing the theoretical literature on the defining characteristics of religious fundamentalism, which will be tied together with two specific case studies: Protestant fundamentalism and Islamic fundamentalism. It will be shown that religious fundamentalism is a defensive strategy employed in response to the uncertainties and rapid shifts of modernity.