Evaluation is usually an internalized process that is intrinsic to the activities of market actors. Producers evaluate what goods to produce, intermediaries such as distributors and retailers evaluate what goods to promote and stock, while consumers evaluate what goods to buy. In some cases, however, a secondary evaluation market controlled by an external evaluator can emerge as a de-facto gatekeeper exerting a powerful influence over the activities of market actors in the primary market. This article develops a conceptual model of external evaluation that describes: (i) the factors common to primary markets that are dominated by evaluation markets; (ii) the characteristics common to dominant evaluators and their evaluation markets; and (iii) the dynamic processes through which an evaluator can become entrenched in a position of dominance over other market actors. This conceptual model is illustrated through examples drawn from three dominant evaluators and the markets they dominate.