This article explores the constitutional provisions that define the role of Islam and the shariah in Afghanistan’s many constitutions. It highlights that successful Afghan constitutions have always recognized Islam and the shariah and established a method of realizing them, while leaving open the possibility that the government could change its approach to realizing them in the future. Unsuccessful Afghan constitutions, by contrast, have allowed actors at the center to try to realize and interpret Islam in a rigid way that does not allow for ongoing negotiations with actors who would prefer to realize and interpret Islam in a different manner. In other words, Afghanistan’s longest-lived and successful constitutions have not entrenched Islam in a way that imposes the desires of one side of the debate. Instead, they have designed religious provisions in vague and ambiguous terms, thereby deferring to the future the question of what Islam really means and how it should be realized in practice – a strategy that proved considerably effective in preventing conflict over the role of Islam in a severely divided and heavily armed society. Drawing on this insight, the article explores how in overwhelmingly, but diversely, Muslim societies, it is important to create constitutional regimes that recognize Islam but leave room for rival interpretations of Islam. Incremental constitution writing is a useful tool in creating such constitutional regimes.