This document provides an overview of capital structure concepts and theories. It defines capital structure as the mix of owned and borrowed capital used to finance a company's assets. Several capital structure theories are described, including the Net Income Approach, Net Operating Income Approach, Modigliani-Miller Approach, and Traditional Approach. The Net Income Approach suggests that leverage can increase firm value by lowering the weighted average cost of capital. However, the Net Operating Income Approach and Modigliani-Miller Approach argue that capital structure does not affect firm value. Finally, the Traditional Approach proposes that an optimal capital structure exists where leverage initially lowers costs but increases risk at higher levels.