The Market Participant Doctrine is a legal principle in U.S. constitutional law that allows state governments to set conditions on transactions when they are acting as buyers or sellers in the marketplace, rather than as regulators. Under this doctrine, states can favor their own residents or impose restrictions that would otherwise be unconstitutional if enacted as regulations. The doctrine provides an exception to the Dormant Commerce Clause, which generally prohibits states from discriminating against or unduly burdening interstate commerce. In cybersecurity, this doctrine can impact how states procure technology and set cybersecurity requirements for vendors when the state is a direct participant in the market.