Multiple Listing Service (MLS), as defined by the National Association of Realtors®, is intended to serve as "a facility for the orderly correlation and dissemination of listing information so participants may better serve their clients and customers and the public," "a means of enhancing cooperation among participants," and as "a means by which authorized participants make blanket unilateral offers of compensation" among other functions. Today there are over 800 MLSs operating across the country, most of them governed by or affiliated with local Realtor® trade associations.¹

Wikipedia states that MLS is a group of private databases which allows real estate brokers representing sellers under a listing contract to widely share information about properties with real estate brokers who may represent potential buyers or wish to cooperate with a seller's broker in finding a buyer for the property.²

The Multiple Listing Service (MLS) began as a periodic publication (MLS Book) designed to allow the listings of broker or agent members to be distributed to large numbers of other member brokerages and agents.  Today, the MLS is an Internet service, which is accessed by all member brokers and agents to list or to search for properties on behalf of their clients.  Therefore, MLS listings enjoy extensive exposure. 

In some states, more than one listing service may exist; some covering certain cities, surrounding areas or counties.  On January 1, 1993, the MLS rules were changed to give sellers the option of offering sub-agency.  Sellers are permitted to offer cooperation to participating members, regardless of whether they are subagents. 

According to the Swanepoel Trends Report the existing MLS model in use today dates back to the 1960s when almost all brokers involved in transactions represented the seller; either as the seller’s agent or as the subagent of the listing broker. The seller paid listing broker and they in turn were responsible to compensate the broker working with the buyer. This all changed during the 1990s with the evolution of buyer’s agents, the advancement of the Internet and the subsequent and rapid sharing of real estate listing data on it.³

More than just a data warehouse, MLSs are marketplaces for showcasing housing prices and amenities. They have been cooperatives that provide neutral ground on which industry competitors cooperate and marketing portals which disseminate listing information.  MLS organizations also provide the central security that monitors the quality of property information while guarding private information about listed properties.

The ownership of MLS information - the compilation of different information sets provided by different parties – has now led to the debate about what elements of a listing can and cannot be protected. It is a generally accepted fact that the raw information pertaining to the property such as number of bedrooms, the square footage, etc. cannot be protected under copyright laws, thereby making it fair game to freely roam the Internet.

MLS Consumer Website Effectiveness Study
Fidelity National Real Estate Solutions
MarketLinx