California Code, Civil Code - CIV § 1087

A multiple listing service (MLS) is a facility of cooperation of agents and appraisers, operating through an intermediary that does not itself act as an agent or appraiser, through which agents establish express or implied contracts for compensation between agents that are MLS participants in accordance with its MLS rules with respect to listed properties in a listing agreement, or that may be used by agents and appraisers, pursuant to the rules of the service, to prepare market evaluations and appraisals of real property.