The article advances the argument that Islamic law, more than a mere legal system, represents a legal tradition. A legal tradition stands at the heart of civilisations generally, and Islamic civilisation particularly. Constitutional design in Muslim states must have this backdrop in mind because modern constitutionalism is typically carried out within the framework of modern nation-states, instead of civilisations. The danger then is that the constitution may end up as a kind of “fiat constitution”. By excavating the historical and philosophical foundations of the modern constitution, the article then shows that the very idea of constitutionalism itself actually accommodates the idea of legal tradition, but unfortunately in practice, it is often ignored when designing the constitution of Muslim states. The article also identifies six core constitutional fault lines of contemporary Islamic civilisation, areas which are most vulnerable to conflicts.