Refers to the structure of an industry or market, as reflected in the number and size distribution of sellers and buyers, the degree of physical or subjective differentiation distinguishing competing sellers' products, the presence or absence of barriers to the entry of new firms, the degree to which firms are vertically integrated from raw material production to retail distribution, the extent of firms' product line diversification, and cost structures. Market structure affects market conduct, which in turn determines market performance characteristics that are the goal of competition policy.

The way that suppliers and demanders in an industry interact to determine price and quantity. There are four main idealized market structures that have been used in trade theory: perfect competition, monopoly, oligopoly, and monopolistic competition.

The degree of competition in a market, ranging from many buyers and sellers to few or even single buyers or sellers.