John Locke was considerably interested and actively involved in the promotion of Protestant Christianity among American Indians and African slaves, yet this fact goes largely unremarked in historical scholarship. The evidence of this interest and involvement deserves analysis—for it illuminates fascinating and understudied features of Locke's theory of toleration and his thinking on American Indians, African slaves, and English colonialism. These features include (1) the compatibility between toleration and Christian mission, (2) the interconnection between Christian mission and English geopolitics, (3) (...) the coexistence of ameliorative and exploitative strands within Locke's stance on African slavery, and (4) the spiritual imperialism of Locke's colonial vision. Analyzing evidence of Locke's interest and involvement in Christian mission, this article brings fully to light a dimension of Locke's career that has barely been noticed. In so doing, it also illustrates how the roots of toleration in the modern West were partly evangelical. (shrink)