Secularization and secularism are closely related concepts that attempt to explain processes and phenomena in politics and public life in the modern era relating, in part, to the differentiation of religion from other aspects of human activity. They are not, however, simply concerned with the distinction between the religious and the secular. Rather, secularization and secularism possess their own particular formations of power, endeavoring to construct specific kinds of ethics, political institutions, and political subjects. They can convey a variety of meanings. However, these may be broadly grouped into two main categories. For secularization, these categories are secularization as a process and secularization as a theory. For secularism, these may be conceptualized as secularism as a form of statecraft or policy and secularism as an ideology. The entry explores various aspects of these approaches to the concepts of secularization and secularism.