Despite the declining salience of divisions among religious groups, the boundary between believers and nonbelievers in America remains strong. This article examines the limits of Americans' acceptance of atheists. Using new national survey data, it shows atheists are less likely to be accepted, publicly and privately, than any others from a long list of ethnic, religious, and other minority groups. This distrust of atheists is driven by religious predictors, social location, and broader value orientations. It is rooted in moral and symbolic, rather than ethnic or material, grounds. We demonstrate that increasing acceptance of religious diversity does not extend to the nonreligious, and present a theoretical framework for understanding the role of religious belief in providing a moral basis for cultural membership and solidarity in an otherwise highly diverse society.