This paper studies the optimal maturity structure for government debt when markets for liquidity insurance are incomplete or non-competitive. There is no fiscal risk. Government debt in the model solves a dynamic inefficiency. Issuing debt in short and long maturities solves a liquidity insurance problem, but optimal yield curve policy is only possible if long-duration debt is rendered illiquid. Optimal policy is implementable through treasury operations only--adjustments in the primary deficit are not necessary.