A two-country differentiated duopoly model is set out in which economic integration increases firms' incentives to invest in R&D, purely through the effect of increased intensity of competition between firms. The model is extended to incorporate knowledge spillovers, which, if related to the degree of integration, give rise to an inverted u-shaped relationship between R&D incentives and integration. The model is also extended to the n-firm general equilibrium case in which integration stimulates economic growth through intensity of competition. As such, the model suggests a positive growth effect of economic integration that does not rely on the usual scale effects