Capital structure decisions are a crucial aspect of corporate finance, balancing debt and equity to optimize a company's financial health. This unit explores the mix of financing sources, their impact on risk and returns, and the factors influencing optimal capital structure. The Modigliani-Miller theorem provides a theoretical foundation, while real-world considerations like taxes, financial distress costs, and agency issues shape practical decisions. Understanding these concepts is essential for managers and investors in evaluating and optimizing a firm's capital structure.