In this paper, we review the most important and representative capital structure models. The capital structure models incorporate contingent claim valuation theory to quantitatively analyze prevailing determinants of capital structure in corporate finance literature. In capital structure models, the valuation of corporate securities and financial decisions are jointly determined. Most of the capital structure models provide closed-form expressions of corporate debt as well as the endogenously determined bankruptcy level, which are explicitly linked to taxes, firm risk, bankruptcy costs, risk-free interest rate, payout rates, and other important variables. The behavior of how debt values (and therefore yield spreads) and optimal leverage ratios change with these variables can thus be investigated in detail.