The functional method has become both the mantra and the bête noire of comparative law. For its proponents it is the most, perhaps the only, fruitful method. For its opponents, it represents everything bad about mainstream comparative law. This chapter tries to reconstruct and evaluate functionalist comparative law by placing it within the larger framework of other disciplines, especially the social sciences. Such an interdisciplinary analysis yields three promises. First, the interdisciplinary look makes possible a (re-) construction of a more theoretically grounded functional method of comparative law than is usually presented. Second, the interdisciplinary approach helps formulate and evaluate the concept in order to determine how functional the method really is. Third, comparison with functionalism in other disciplines can reveal what is special about functionalism in comparative law, and why what in other disciplines would rightly be regarded as methodological shortcomings may in fact be fruitful for comparative law. This opens the way to a reformulated functional method of comparative law.