In this paper we consider the impact of vertical integration on a retailer's choices of product variety and specific, brand-supporting investment. In an incomplete contract environment, vertical merger encourages investment in integrated supply, and foreclosure of non-integrated manufacturers. Anti-competitive as opposed to efficiency interpretations depend delicately on a trade-off between the benefits of supplier-specific rather than generally applicable retailer investment, and the value of multi-product rather than single product retailing. Where retailers compete, it is shown that vertical integration implements competition reducing, product differentiating investment strategies.