The code Napoleon has been one of the first (on such a scale), the most important and the most pervasive processes of codification that ever took place. The purpose of our paper is to provide an economic analysis of the making of this codification. We compare customary codification and contractual codification: while the former amounts to the crystallisation of socially accepted practices, the latter consists in a creation of rules through a writing process. These theoretical differences are less clear-cut when history mixes practices and reasoned arguments. We then show that the making of the code Napoleon reflects it since it borrows from the social contract and the spontaneous order traditions.