Trade and market are interdependent. Oboe trade without a market - oboe market without trade. Every person comes into contact with trade and market, yet there is hardly any conscious engagement with these phenomena. They are taken for granted. Therefore, the aim of this textbook is to clarify the functioning of trade, market, and market economy, as well as their interdependencies. The title "Market Economy Theory of Trade" serves as both a content announcement and a program. Trading companies and their associations do not only operate in markets - they are also markets themselves and they create markets and competition. They are simultaneously organs and organizers of the market economy, as well as subjects of state market policy. Due to this interconnection, the usual separation into business or economic fields is abolished.