This article addresses Pakistani Islamists' street power — their ability to organize rallies, protests, and demonstrations. Building on research on religion and collective action, I first demonstrate how Friday prayers aid Islamist mobilization. Mosques on Friday serve as a filtering and coordination tool, as tactical “choke” points in urban neighborhoods, and as incitement through the imam's sermon. I then show how Islamist street power affects Islamization in Pakistan. I argue that Pakistan's foundational religious nationalism acts as an “opportunity structure,” and affords Islamists agenda-setting and veto power. The success of Islamist agitation depends on the issue contested, the type of regime targeted, and the era in which it is practiced. I use interviews, participant observation at Islamist rallies, an original dataset of all rallies and protests in Pakistan from 2005 to 2010 (n = 4123); and government and local newspaper reports from the 1940s onward to buttress my claims.