This article examines the origin and legacy of the rebel group that stormed the great Mecca mosque in November 1979. Extensive fieldwork and new primary sources show that the rebels represented a radicalized faction of a large pietistic organization established in Medina in the mid–1960s under the name al–Jama a al–Salafiyya al–Muhtasiba (JSM). The rebel faction had broken with the mother organization in 1977 and developed into an apocalyptic sect under the leadership of Juhayman al–Utaybi, who spent two years as a fugitive in the desert before the attack. Although the rebellion was crushed, the early 1990s witnessed a resurgence of Juhayman's ideas in Saudi Arabia. The article argues that the JSM, the Mecca rebels, and their heirs represent a widely ignored undercurrent of Saudi Islamism. Pietistic and isolationist, this so–called rejectionist Islamism is intellectually and sociologically distinct from the two other strains of Saudi Islamism, namely, reformism and jihadism.