Mormonism, rooted in the 1820s and 1830s by Joseph Smith in Western New York, is the religious tradition of the Latter Day Saint movement within Restorationist Christianity. The term "Mormonism" has been used to describe various aspects of this movement, although the Church of Jesus Christ of Latter-day Saints (LDS Church) has recently distanced itself from the label. Historian Sydney E. Ahlstrom's 1982 quote captures the complexity of Mormonism, which has been considered a sect, mystery cult, new religion, church, people, nation, and American subculture at different times and in different places.

A significant aspect of Mormon theology is the Book of Mormon, which presents itself as a chronicle of early Indigenous peoples in the Americas and their interactions with God. Mormon theology combines mainstream Christian beliefs with unique elements derived from revelations to Joseph Smith and other religious leaders. It incorporates various religious texts, including the Bible, Doctrine and Covenants, and the Pearl of Great Price. Key doctrines include eternal marriage, eternal progression, baptism for the dead, polygamy (which the Utah-based LDS Church banned in 1890), sexual purity, dietary guidelines (Word of Wisdom), fasting, and Sabbath observance. Mormon theology is not uniform, with various groups emerging, differing in their views on polygamy and Trinitarianism. Those practicing polygamy are associated with Mormon fundamentalism, while other groups affirm Trinitarianism and describe themselves as Trinitarian Christian restorationists, such as the Community of Christ. Additionally, there's a concept known as "Cultural Mormonism," coined by cultural Mormons who embrace the culture without necessarily adhering to the theology.