One of the largest Protestant denominations, with 40 million members (and many more non-member adherents) worldwide and 26. 7 million in the United States. The Baptist tradition has its roots in the Anabaptist movement of the Reformation and English Puritan John Smyth (1554-1612). Its most notable distinction is its rejection of infant baptism. Today, most Baptists in American belong either to the Southern Baptist Convention or the American Baptist Convention. See Comparison Charts of Christian Denominations for more information.