Spiritualism is a monotheistic belief system or religion, postulating a belief in God, but with a distinguishing feature of belief that spirits of the dead residing in the spirit world can be contacted by "mediums", who can then provide information about the afterlife.^[59]

Spiritualism developed in the United States and reached its peak growth in membership from the 1840s to the 1920s, especially in English-language countries,^[60][61] By 1897, it was said to have more than eight million followers in the United States and Europe,^[62] mostly drawn from the middle and upper classes, while the corresponding movement in continental Europe and Latin America is known as Spiritism.

The religion flourished for a half century without canonical texts or formal organization, attaining cohesion by periodicals, tours by trance lecturers, camp meetings, and the missionary activities of accomplished mediums. Many prominent Spiritualists were women. Most followers supported causes such as the abolition of slavery and women's suffrage.^[60] By the late 1880s, credibility of the informal movement weakened, due to accusations of fraud among mediums, and formal Spiritualist organizations began to appear.^[60] Spiritualism is currently practiced primarily through various denominational Spiritualist Churches in the United States and United Kingdom.