This document summarizes the Capital Asset Pricing Model (CAPM). It begins by outlining the key assumptions and logic behind the CAPM. The CAPM builds on Harry Markowitz's portfolio choice model by adding assumptions of a risk-free rate and market clearing prices. This implies that the market portfolio must be mean-variance efficient. The CAPM then predicts that an asset's expected return is determined by its beta, or non-diversifiable risk relative to the market. However, the document notes that empirical tests have found the CAPM performs poorly in validating these predictions. It concludes that while theoretical or implementation issues may be to blame, the CAPM's failure in empirical tests means its applications are generally invalid.