The document discusses efficient portfolios and the single index model. It defines efficient portfolios as those with the smallest risk for a given level of expected return or largest expected return for a given level of risk. The single index model assumes the risk of return from each security has two components: the market-related component and a company-specific residual error component. It provides an equation to model the return of a security based on its sensitivity to market returns and a residual error term. The model can also be applied to portfolios to find the minimum variance set of portfolios. Finally, it mentions analyzing a portfolio of 10 companies to determine which provides maximum return with minimum risk using the single index model.