The document discusses two theories of capital structure - the pecking order theory and the trade-off theory. The pecking order theory states that firms prefer internal financing, then debt, and lastly equity if external financing is needed. This is due to problems with adverse selection and managerial preference for internal funds. The trade-off theory views capital structure as a trade-off between tax benefits of debt and costs of financial distress, predicting an optimal debt level where benefits equal costs. The document provides details on both theories and their implications for company financing decisions and performance.