<p>Dina and Formal Law in Madagascar: Transaction Costs and Institutional Coexistence</p>

Madagascar's Dina are community rules whose contemporary operation unsettles a simple distinction between formal and informal institutions. Some Dina remain socially enforced local conventions; others are incorporated into statutory arrangements, approved by courts, or embedded in contracts that transfer natural-resource management to communities. This article develops a comparative institutional model of that coexistence. Compliance depends on legal enforcement, community sanctions, and the local legitimacy that sustains monitoring and reputation. Institutional performance also varies with group size because community governance economises on access and information costs at small scale but faces rising coordination costs as the relevant population expands. Legal recognition can therefore complement rather than replace local enforcement, although stronger state standardisation may weaken compliance when it displaces locally generated rules. The model yields conditions for a scale threshold, an interior level of legal recognition, and evolutionary stability of community governance. Evidence from Madagascar's natural-resource legislation and studies of forest and marine governance anchors the assumptions and clarifies their limits. The analysis places the Dina within current debates on institutional complementarity, legal pluralism, and the comparative costs of governance.