The basics of a new theory of economic systems are proposed in this article as a fundamental synthetic field of economics. This theory proposes to unify a description of economic phenomena usually studied by different areas of economics: economic agents, i.e., legal and physical entities, formal and informal institutions, economic processes, and projects. A basic classification of economic systems is developed, their key functions are defined, and the need for power parity of the basic types of economic systems is proved. The results obtained are used to classify the types of national economic policy and elaborate measures aimed at preventing crisis phenomena and building a well-balanced economy.