The Bible Belt is an informal term for an area of the United States of America in which socially conservative Evangelical Protestantism is a dominant part of the culture. In particular, in the United States it is an idiom for the region where the Southern Baptist Convention denomination is strongest (though many other denominations, such as the Church of Christ and Assemblies of God, can be found there as well)—usually meaning the South and nearby areas.

Much of the Bible Belt consists of the Southern United States. During the colonial period (1607-1776), the South was a stronghold of the Anglican church. Its transition into a conservative Protestant Bible Belt occurred gradually over the next century, as a series of religious revival movements, many associated with the Baptist denomination, gained great popularity in the region.

The region is usually contrasted with mainstream Protestants and liberal Catholics of the northeast and Great Lakes, the religiously diverse Midwest, the Mormon Corridor in Utah and southern Idaho, and the relatively secular western United States. The percentage of non-religious people is the highest in the northwestern state of Washington at 27%, compared to the Bible Belt state of Alabama, where it is 6%.

The earliest known usage of the term "Bible Belt" was by American journalist and social commentator H.L. Mencken, who wrote: