At first glance, it appears that residents across the Middle East and North Africa have increasingly mobilized along ethnic, religious, and sectarian lines in the wake of the so-called Arab Spring. Kurds, for example, have mobilized in and across Syria, Turkey, and Iraq; Shia protested in Bahrain and Saudi Arabia and are fighting for control of the state in Yemen. Ethno-sectarianism appears pervasive in the MENA, arguably replacing ideological fault-lines. But, such a perspective ignores the many ethnic and religious “groups” that have not mobilized in new ways in recent years, such as Shia in Kuwait, Egypt, and the UAE; Berbers in much of North Africa; and Druze in Syria. In much of the region, ethnic and sectarian identities do not translate into mobilization. This paper evaluates patterns of and changes in ethno-sectarian mobilization throughout the MENA by focusing not just on groups that have mobilized but by also considering those that have not. An original dataset of ethnic and religious groups in the region is presented and analyzed to see where and when those latent identities became mobilized. It finds that the vast majority of currently mobilized ethno-sectarian groups were mobilized prior to 2011. Relatively few previously un-mobilized groups became mobilized. The paper then turns to a series of paired case studies, examining groups that mobilized alongside those that did not, to determine what factors may explain the difference. Key cases examined include Kurds in Iran, Shia in Kuwait, and Berbers in Libya. The findings have important implications for how we conceptualize and analyze ethnic politics and sectarianism, transnational diffusion, and the misleading idea of a “Shia revival” or crescent. The paper concludes with a brief methodological discussion of different ways in which collective mobilization is often studied and the inferential risks various approaches pose.