The market portfolio

The market portfolio is a combination of the whole market’s investments, including the risk-free investment. These are weighted by their presence in the market. Investors should hold the market portfolio because it gives the highest expected return for a given level of risk, as well as the lowest risk for a given expected return. In order to attain a true market portfolio of investments, investors would need to invest in every single asset available, which is unrealistic and therefore a limitation of this theory. To create a portfolio with the risk and return profile of the market portfolio, investors usually purchase a representative group of assets in order to mimic the market as a whole.