We examine the Nash equilibria of a game where two national governments set patent breadth strategically. Broader patents make R&D more attractive, but the effect on static efficiency is nonmonotonic. In a North–South model, where only the North can innovate, harmonization of patent breadth lowers welfare relative to the Nash equilibrium. When both countries can innovate, harmonization toward narrower patent breadth may raise world welfare. (JEL F02, F13, O3, O31, O32)