The Multiple Listing Service is first and foremost a list of virtually all properties for sale in a particular area. It is also an offer of compensation between brokers. Basically this consists of listing brokers telling other brokers, ?You bring me a buyer and I will pay you a portion of the total commission.? It spells out the exact amount, many times either two and one half or three percent of the gross sales price. The Multiple Listing Service is also the listing data source for numerous Internet websites such as Realtor.com, local newspaper sites, or other broker websites. While browsers cannot view full detailed information on the listings, they can at least obtain a snapshot. Being the main source for property information across the Web has made the Multiple Listing Service that much more powerful in the information age.

It is important to note that Multiple Listing Services generally have a geographic monopoly on a particular area. For instance, the SoCal MLS is ?the? MLS for Orange County, California. The Northwest MLS is the only MLS that a property in the Seattle, Washington area needs to be listed in. The Tucson Association of Realtors MLS is the place listing agents, buyers agents, sellers, and buyers turn to in Tucson, Arizona. Across the country there are over 700 Multiple Listing Services. Occasionally there is consolidation between smaller MLS's, but many small Realtor associations continue to be associated with one equally small MLS with no intentions of expanding or consolidating. These local associations like having control over the way data is entered and presented in their MLS, they like not answering to a separate organization in a larger city, and they like having their own lockbox system. Frankly, they may also like that a Realtor in, for instance, a large city like Phoenix cannot drive 90 miles to Payson, Arizona, and list, show, and sell properties just like a local agent (without joining the local Central Arizona Board of Realtors Multiple Listing Service).

The offer of compensation between brokers is a fundamental aspect of the Multiple Listing Service. Unlike showing For Sale By Owner properties whereby a broker would need to negotiate with each individual homeowner a compensation agreement, in the case of MLS-listed properties, a broker can show numerous properties knowing exactly in advance how much compensation is being offered. This is extremely comforting and time-saving to the broker. Since brokers representing buyers sometimes have the buyer sign a buyer's agency agreement guaranteeing that broker a minimum commission (such as three percent), they can also know in advance what amount, if any, the buyer will need to come out of pocket with prior to viewing a property. If the compensation offered required the buyer to come up, for instance, ten thousand dollars extra on top of the sales price, the buyer may elect to pass over the property in favor of ones which required no extra money be paid. Thus offering competitive compensation to other brokers can enable additional showings.