The efficient boundary is the set of securities that can get the maximum profit with the minimum risk under the income-risk constraint. On the efficient boundary, we can get a series of high-risk and high-return portfolios (that is, the combination of positive special relationships).

1952, markowitz published a paper entitled "The Choice of Portfolio". In the first article, a mathematical model is used to analyze the portfolio, which makes this revolutionary scientific method have a great influence on the theory of reporting capital. The goal of asset selection analysis is to find the most effective portfolio set, that is, the effective frontier of investment.

Markowitz's portfolio theory has long been proved to be effective in practice and has been widely used in portfolio selection and asset allocation. Based on markowitz's portfolio analysis, many investors recommend optimization and portfolio according to their income and risk preferences.

In Markowitz mean variance model, each security or portfolio can be represented by a point in the mean variance coordinate system, so all existing securities and legal portfolios form a region on the plane, which is called feasible region, the top of the left boundary of the feasible region is called effective boundary, and the portfolio corresponding to the point on the effective boundary is called effective portfolio.