This document discusses the weighted average cost of capital (WACC), which is a calculation of a firm's cost of capital using weighted average costs of the different capital components (equity, debt, etc.). It outlines how WACC is calculated using either marginal weights based on new capital raised or historical weights based on book or market value. Market value weights are preferred because investors require market rate of return on market value, not book value, of capital. The document provides an example calculation of WACC using market value weights of equity, preferred stock, and debt. It concludes by listing the WACC and debt weight for some large corporations.