We review methodological aspects of credit-risk models in the literature and their implications on credit-risk spreads. We have chosen five of representative structural models: Merton (1974), Longstaff and Schwartz (1995), Leland and Toft (1996), Collin-Dufresne and Goldstein (2001), and Chen, Collin-Dufresne and Goldstein (2009). Recent structural models suggest that credit risk spreads can be greatly influenced not only by the loss distribution of risky corporate securities but the representative investor's consumption habit formation, and by interaction between default losses and macroeconomic factors such as market prices of risk and stochastic interest rates.