Topicality. As is known, the economic theory is based on the fact that any economy is based on production and consumption of good and benefits that are necessary for people's lives. At that, economy is based on people's needs and economic interests, which make them act in one way or another. As a result, there appear relations of production (creation), exchange, consumption, and acquisition of life goods, which are called economic relations. It is important to understand that implementation of the needs and interests, which are systemically interconnected, predetermines the existence of not just a totality of public relations but an economic system. Purposes and tasks of the research. The purpose of the research is to study economic relations and economic systems. The authors set the following tasks: studying the notion "economic activities" and its correlation to the notion "entrepreneurial activities"; studying the structure of an economic system; determining the position on the debatable issues that emerge during conduct of the research. Conclusions. The Constitution of the RF formulates the principles of market economy (competitiveness, equality of ownership forms, integrity of economic space, freedom of entrepreneurial activities, etc.), so the Russian economy is a market economy, not mixed economy. Market economy is the most flexible and effective.