A multiple listing service (MLS) is a service used by a group of real estate brokers. They band together to create an MLS that allows each of them to see one anothers listings of properties for sale. Under this arrangement, both the listing and selling broker benefit by consolidating and sharing information, and by sharing commissions.
Most MLSs create a book or an electronic database with all of the houses for sale by affiliated brokers, who update it on a regular basis. The participating parties distribute the book in print or online to each member of the service.