The New Institutionalism in Political Science has not only rekindled an interest in the role of institutions, but also highlighted the distinction between formal and informal institutions. The case of Lebanon allows for a direct comparison of the way in which the institutionalization of power-sharing arrangements affects peace and politics. The National Pact of 1943 was a gentleman's agreement between the leaders of the two main religious communities. It formed the basis for a consociational system that lasted for decades. After the civil war, the Ta"if agreement reintroduced consociationalism, but this time many of the most important institutions were constitutionalized. This article compares the informal consociationalism of the National Pact with the formal consociationalism of the Ta'if Agreement. In doing so, it not only contributes to the consociational literature and the debate about the merits of liberal versus corporate consociations, but also to the New Institutionalism and questions about the relative strength of formal versus informal institutions.