Spiritualism is a social religious movement popular in the nineteenth and early twentieth centuries, according to which an individual's awareness persists after death and may be contacted by the living. The afterlife, or the "spirit world", is seen by spiritualists not as a static place, but as one in which spirits continue to interact and evolve. These two beliefs—that contact with spirits is possible, and that spirits are more advanced than humans—lead spiritualists to the belief that spirits are capable of advising the living on moral and ethical issues and the nature of God. Some spiritualists follow "spirit guides"—specific spirits relied upon for spiritual direction.

Emanuel Swedenborg has some claim to be the father of spiritualism. The movement developed and reached its largest following from the 1840s to the 1920s, especially in English-speaking countries. It flourished for a half century without canonical texts or formal organization, attaining cohesion through periodicals, tours by trance lecturers, camp meetings, and the missionary activities of accomplished mediums. Many prominent spiritualists were women, and like most spiritualists, supported causes such as the abolition of slavery and women's suffrage. By the late 1880s the credibility of the informal movement had weakened due to accusations of fraud perpetrated by mediums, and formal spiritualist organizations began to appear. Spiritualism is currently practiced primarily through various denominational spiritualist churches in the U.S., Canada and the United Kingdom.

Spiritualists believe in the possibility of communication with the spirits of dead people, whom they regard as "discarnate humans". They believe that spirit mediums are gifted to carry on such communication, but that anyone may become a medium through study and practice. They believe that spirits are capable of growth and perfection, progressing through higher spheres or planes, and that the afterlife is not a static state, but one in which spirits evolve. The two beliefs—that contact with spirits is possible, and that spirits may dwell on a higher plane—lead to a third belief, that spirits can provide knowledge about moral and ethical issues, as well as about God and the afterlife. Many believers therefore speak of "spirit guides"—specific spirits, often contacted, and relied upon for worldly and spiritual guidance.

According to spiritualists, anyone may receive spirit messages, but formal communication sessions (séances) are held by mediums, who claim thereby to receive information about the afterlife.

As an informal movement, spiritualism does not have a defined set of rules, but various spiritualist organizations within the United States have adopted variations on some or all of a "Declaration of Principles" developed between 1899 and 1944. In October 1899, a six article "Declaration of Principles" was adopted by the National Spiritualist Association (NSA) at a convention in Chicago, Illinois. An additional two principles were added by the NSA in October 1909, at a convention in Rochester, New York. Then, in October 1944, a ninth principle was adopted by the National Spiritualist Association of Churches, at a convention in St. Louis, Missouri.^{[citation needed]}

In the UK, the main organization representing spiritualism is the Spiritualists' National Union (SNU), whose teachings are based on the Seven Principles.

Spiritualism first appeared in the 1840s in the "Burned-over District" of upstate New York, where earlier religious movements such as Millerism and Mormonism had emerged during the Second Great Awakening. However, Millerism and Mormonism did not associate themselves with spiritualism.

This region of New York State was an environment in which many thought direct communication with God or angels was possible, and that God would not behave harshly—for example, that God would not condemn unbaptised infants to an eternity in Hell.