The Religious Society of Friends, commonly known as Quakers, was founded in England in the 17th century as a Christian religious denomination by people who were dissatisfied with the existing denominations and sects of Christianity. Historians generally credit George Fox with being the principal co-founder or most important early leader. The Society of Friends is counted among the historic peace churches.
Since its beginnings in England, Quakerism has spread to other countries, chiefly Bolivia, Costa Rica, Guatemala, Kenya, Peru, and the United States. The total number of Quakers is relatively small (approximately 350,000 worldwide ), although there are places, such as Pennsylvania (particularly Philadelphia); Newberg, Oregon; Greenleaf, Idaho; Richmond, Indiana; Birmingham, England; and Greensboro, North Carolina in which Quaker influence is concentrated.
Unlike many other groups that emerged within Christianity, the Religious Society of Friends has tended away from creeds, and in modern times away from hierarchical structure.
The various branches have widely divergent beliefs and practices, but the central concept to many Friends is the "Inner Light". Accordingly, individual Quakers may develop individual religious beliefs arising from their personal conscience and revelation coming from "God within"; further, Quakers feel obliged to live by such individual religious beliefs and inner revelations.
Many Quakers feel their faith does not fit within traditional Christian categories of Catholic, Orthodox or Protestant, but is an expression of another way of experiencing God.
Although Quakers throughout most of their history and in most parts of the world today consider Quakerism to be a Christian movement, some Friends (principally in some Meetings in the United States and the United Kingdom) now consider themselves universalist, agnostic, atheist, nonrealist, humanist, postchristian, or nontheist, or do not accept any religious label. Calls for Quakerism to include non-Christians go back at least as far as 1870, but this phenomenon has become increasingly evident during the latter half of the 20th century and the opening years of the 21st century, and is still controversial among Friends. An especially notable example of this is that of Friends who go beyond simply being non-christian, but actively identify as a member of another faith, such as Islam or Buddhism.