We document several facts about corporate debt maturity: (1) debt maturity is pro-cyclical, (2) higher-beta firms tend to have longer maturity, and (3) shorter maturity amplifies the sensitivity of credit spreads to aggregate shocks. We present a dynamic capital structure model that explains these facts. In the model, leverage and maturity choices are interdependent, which reflect the tradeoffs of liquidity discounts of long-term debt, repayment risks of short-term debt, and the benefit of short-term debt as a commitment device for timely leverage adjustments. Additionally, the model helps quantify the effects of maturity dynamics on the term structure of credit spreads.