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What is an MLS and How Many MLSs Are There? Multiple Listing Service FAQ

Frequently Asked Questions About MLSs

Multiple Listing Services (MLS) in the real estate industry are multi-broker organizations that increase access to housing opportunities and drive exposure for property listings. They ensure cooperation between brokers for buyers and brokers for sellers, which is a benefit for consumers.

MLSs are critical to a competitive and transparent marketplace for consumers. The value of these organizations lies beneath the surface of the Internet advertising that most consumers experience. This guide provide answers to common questions about the MLS organization, its brokers, the broker’s consumer clients and the technology that provides a platform for the MLS marketplace.

What is an MLS?
A Multiple Listing Service is an organization that is a collective of brokers. It establishes rules for cooperation in sharing and selling listings. Brokerages (and their agents) joining an MLS agree to abide by rules when working to sell other brokers’ listings, and those brokers agree to do the same in return. 

The MLS setup is unique, in that competitors must cooperate to successfully close transactions. This creates great benefits for consumers. The broker cooperative creates the marketplace that makes buying, selling, renting, and investing in property more transparent and efficient. The MLS organization is the foundation on top of which many technology platforms exist today.

– Want to learn more about MLS data, rules and organizations? See RESO’s Working with Real Estate Data course and earn your RED-B designation.

How many MLSs are there?
As of June 2024, RESO tracks 535 MLS systems in the U.S., 39 in Canada and 9 others in U.S. territories and other parts of the world.


RESO tracks individual MLS systems for certification purposes and as a service to the real estate industry. Some MLSs exist under broader organizational umbrellas called “pooled platforms.” Other industry MLS lists may track at a lower total number if they only count the larger entity (e.g., MichRIC is a pooled platform that contains 14 independent MLSs) or if they only count MLSs affiliated with the National Association of REALTORS® (NAR).

In addition to NAR-affiliated MLSs, RESO tracks unaffiliated MLSs that wish to pursue certification or are certification eligible by virtue of fitting the conditions of a multi-broker organization that exists as an open system that has relationships with technology vendors and includes certifiable elements like the RESO Data Dictionary, Web API or RESO Common Format (RCF). 

Definitions: Certified Legacy (on an older standard), Passed Current (technical testing is done), Certified Current (certification terms have been accepted).

The number of U.S. MLSs tends to shrink annually due to regional consolidation of MLSs. New MLSs are being created in Mexico, the Caribbean, Central America, South America, Europe and West Asia. Most countries do not yet have the broad market share that North American MLSs have, but projects like the RESO-supported International MLS Forum are bringing MLS and RESO concepts to a wider audience that is already part of a global marketplace.

RESO manages MLS counts as part of its Unique Organization Identifier (UOI) service. The UOI is an ID system that tracks active and inactive MLSs as well as REALTOR® associations, technology vendors, pooled platforms and more. The UOI is updated regularly and will continue to grow to cover brokerages and other real estate-related businesses. The certification status of organizations covered by the UOI are recorded on the RESO Certification Map. UOI as Spreadsheet | UOI in JSON | Data updated 07/12/2024.

When did MLSs get started?
MLSs were first created in the late 1800s, far before computer or Internet technology existed. In-person listing sharing, paper notes, index cards and printed MLS books all preceded the online MLSs that we experience today.

Who belongs to the MLS?
Real estate brokers in a shared marketplace form and join an MLS. Brokerage organizations that cross over multiple marketplaces will often join multiple MLSs.

Who are participants and subscribers in an MLS?
Brokers in an MLS are called participants. Agents in an MLS are called subscribers. Agents generally cannot join an MLS unless their broker does so first. 

How can I list my home on the MLS?
Homeowners can work with a real estate broker to list their homes on the MLS. Only participating brokers can list properties on the MLS.

Why should I list my home on the MLS?
The MLS exposes a listing to every broker in the marketplace who may be working with buyers in search of this kind of property. This can include Internet marketing that brokers approve through the MLS. Even listings that need privacy can be excluded from Internet marketing yet still be delivered to the MLS’s brokers for more discreet exposure to potential buyers.

Is the MLS a database?
The MLS has a database, but the MLS is not just a database. The organization and its cooperative broker rules allow for a listing database to be created and shared between participating brokers.

Are websites like,,,, and MLSs?
No. These are popular websites that get some of their listing data from MLSs, but they are not MLSs themselves. They are considered advertising portals and brokerage websites with permission to display real estate listings. These organizations are all RESO members who contribute to the development of data standards that drive MLS technology innovation.

Why are there multiple MLSs in the same marketplace?
MLSs that formed from local associations can grow and sometimes overlap in other MLS marketplaces. They are not constrained by geography. Competitive MLSs will sometimes share data or merge, but many markets still have duplication of services with multiple MLSs.

Who owns the MLS?
Most MLSs are owned by the REALTOR® association that formed them. They may be owned by multiple associations in a regional MLS. Some MLSs were formed directly by groups of brokers which own the MLS themselves.

Who runs the MLS?
MLSs are managed in a number of ways. Some REALTOR® association-owned MLSs are managed by association staff. Others are split off as separate organizations with separate staff from the association. Independent MLSs usually derive their management strategy and operations from the brokers who formed the cooperative.

Who can join an MLS?
For REALTOR® association-owned MLSs, brokers often have to be REALTOR® members before they can join the MLS. This is not true in all cases, as some states have regulations that require non-REALTOR® brokers to be allowed to participate in the MLS. Any broker can join an independent MLS. Real estate agents join the MLS under the umbrella of a participating broker.

What are the rules for participating in an MLS?
Participating brokers agree that they will share their listings with the MLS’s other participating brokers. They must abide by the MLS’s rules to act cooperatively and honestly in representing buyers and sellers through transactions with their competitors.

Who sets the rules for the MLS?
Each MLS sets some of its own local rules. For REALTOR®-owned MLSs, there are also overarching policies and rules that come down from NAR. The NAR Handbook on Multiple Listing Policy documents these mandatory and suggested rules.

What is RESO?
RESO is the Real Estate Standards Organization. RESO creates open standards through its broad industry membership of MLSs, associations, brokers and technology companies. Similar to standards like Wi-Fi and Bluetooth, RESO standards drive interoperability between technology products and competitive innovation in the real estate industry. | ABOUT RESO

What does the MLS organization look like?
The MLS is an organization with brokerage leadership, staff, technology vendors, data licensing agreements, rules and regulations, and a compliance department. It can be a very small organization with vendors supplying most of its services or a large organization with in-house staff that supplies all of its organizational and technical needs.

How can I get data from the MLS?
The MLS provides data to its participating brokers. It also provides data to technology partners, with the approval of its broker membership. Some MLS data that is deemed to be helpful for consumers is displayed without cost to the public on broker and MLS websites.

Is the Web API the way I get data from an MLS?
The way MLSs transport data to their brokers and technology partners varies. The most modern and efficient way is through the RESO Web API standard. RESO does not supply the data or the service, just the standard model for it. MLSs provide their own Web API services to deliver data to their customers.

Which MLS data is public and which is private?
Public MLS data is usually that which a consumer would use to learn about a listing for sale. Property information, media and agent marketing comments are usually public. Private information about sellers and agent-only showing instructions are usually held privately by the MLS’s broker participants.

Why are there so many MLSs?
MLSs were first created before computer technology. Local REALTOR® associations and brokers would come together and share listings in their local marketplaces. They created more than 1,000 local marketplaces and didn’t feel the need at the time to have large regional real estate cooperatives.

As technology efficiency and a mobile population have made regional and national databases of real estate listings more desirable, MLS organizations continue to consolidate and shrink in numbers.

Are there MLSs in every country?
MLSs are the dominant form of real estate market in the United States and Canada. New MLSs are being created in Mexico, the Caribbean, Central America, South America, Europe and West Asia. Most of the world has not enjoyed the transparent, organized marketplace of the MLS, but its value is becoming evident and efforts to reproduce it globally have significant momentum.

Is the MLS a real estate website?
An MLS may have a website, but that is just one downstream product of the MLS organization. The MLS is not a public marketing platform. It is a cooperative for brokers to share listings with other brokers. The MLS improves the ability of brokers to market their own listings.

Who pays for the MLS?
Brokers and agents usually pay dues to the MLS. This may be directly to the MLS organization or through their REALTOR® association dues.

Does the MLS set commission rates?
An MLS does not take a position on what a broker’s business model is or what commission rates the broker charges. Some MLSs give the option of sellers advertising a financial concession or allowance to the buyer in the listing for the property. But sellers and buyers negotiate the amount of concessions and compensation in their contracts with their brokers and agents outside of the MLS.

Which technology vendors work with which MLSs?
There are about a dozen core MLS software platform technology vendors in North America. These companies get their technology certified by RESO on a regular basis, and those certifications are visible on the RESO Certification Map and in RESO Analytics. MLSs also work with many other accessory technology vendors and provide those services to their members.

What does it mean for an MLS to be certified by RESO?
Being certified by RESO means an MLS’s technology systems can talk to other technology systems in a standardized manner. RESO-certified systems are interoperable, meaning they speak a universal language of standards. Just as with Wi-Fi or Bluetooth, a standard language means many technology companies can build new products that will work together, making life for brokers, agents, consumers and technology companies much easier and accelerating new technology innovation. 

Is my MLS RESO certified?
You can review the certification status of all MLSs on the RESO Certification Map and in RESO Analytics.

What are cooperation and compliance within the MLS?
Cooperation means sharing listings and abiding by the rules to cooperatively list, show, negotiate and sell listings with competitors. Compliance is the enforcement of MLS rules by MLS staff to ensure an orderly and fair marketplace.


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