Abstract This paper analyzes the role of financial intermediaries as marketmakers in the market for interest rate swaps. We argue that intermediaries which hold large nontraded portfolios of swaps are efficient alternatives to direct hedging by counterparties in publicly traded cash and futures instruments. The efficiency afforded by the swap marketmaker derives from reduction in transactions costs, diversification of basis risk, and reduced agency costs of debt. The analysis provides an explanation for the existence and success of the swaps market as a means for spreading risk and for its dominance by large financial institutions.