Fundamentalism is a tendency among certain groups and individuals that is characterized by the application of a strict literal interpretation to scriptures, dogmas, or ideologies, along with a strong adherence to traditional beliefs and practices. It is a conservative religious movement that advocates for strict conformity to sacred texts. The term "fundamentalism" was first used by American Christian groups to describe their own stance as opposed to what they perceived as the liberal and irreligious tendencies of modern science and theology.

Fundamentalism is often associated with a reaction against aspects of modernity, such as secularism, liberalism, and ecumenism, which it perceives to be foreign to a particular religious tradition. It is also often characterized by a militant rejection of secular modernity and an inherently political phenomenon, seeking to remake all aspects of society and government on religious principles.

There are varying degrees of overlap between fundamentalism and (radical) nationalism, and different types of fundamentalism exist. For example, Christian fundamentalism is a movement within the church that holds to the essentials of the Christian faith, while Islamic fundamentalism is a movement that seeks to establish Islamic law as the basis of society and government.

The term "fundamentalism" can be a pejorative rather than a neutral characterization, similar to the ways that calling political perspectives "right-wing" or "left-wing" can have negative connotations. However, it is important to note that fundamentalism is not inherently negative or positive, but rather a complex phenomenon that can have both positive and negative effects.