Flat Fee MLS generally refers to the practice in the real estate industry of a seller entering into an "à la carte service agreement" with a real estate broker who accepts a flat fee rather than a percentage of the sale price for the listing side of the transaction. The buyer's broker is still typically offered a percentage though that could be a flat fee as well. A Flat Fee MLS brokerage typically unbundles the services a traditional real estate brokerage offers and lists the property for sale in the local Multiple Listing Service (MLS) à la carte without requiring the seller to use its services for valuation assistance and showing accompaniment.

The real estate brokerage industry is evolving to accommodate modern consumer demands. The Department of Justice, in a letter to Governor Bill Blunt of Missouri dated May 23, 2005 provides a summary of these changes. The reference cited for this excerpt is a letter written by the DOJ to encourage Governor Blunt to veto a bill that, according to the DOJ, would have reduced consumer's options and increased the cost of selling real estate.

In a flat fee MLS listing, the listing agreement between the real estate broker and the property owner typically requires the broker to enter the property into the MLS and provide other contracted services, with the broker acting as what the traditional industry has coined a "limited service broker". Currently there are numerous descriptions used to describe reduced fee and discounted real estate services, some of which are not based on providing limited services.

The Department of Justice uses terms such as "nontraditional", "Fee-For-Service", and "menu driven", which are in contrast to "traditional" real estate service(s) offered by a licensed real estate broker to a seller of real estate. It is important that the consumer understand there is not currently any standard terminology for nontraditional real estate services though à la carte is probably the best description.

The flat fee MLS service is radically different from traditional real estate brokerage services. Because every State requires a listing agreement between a real estate broker and property owner, the rapid explosion of flat fee service providers has created a gap in the States developing laws governing flat fee services provided by real estate broker. In most real estate board / MLS systems, there are generally two types of listing agreements, although some Boards allow others. The first and most common is called an "Exclusive Right to Sell" listing, in which the seller will not only pay a commission if their property is sold through their listing broker or another MLS broker (buyer's broker), but also if the seller finds their own buyer. In an "Exclusive Right to Sell" listing, the listing broker gets the commission specified in the listing agreement regardless of who actually finds the buyer. The second type of listing agreement is called an "Exclusive Agency" listing agreement. This "Exclusive Agency" is one form of agreement that can be used to allow the seller to market their property "By Owner" and pay zero commission if they are successful in finding their own buyer. It is this "Exclusive Agency" listing agreement that forms the basis for many flat fee service providers’ listing agreements. In essence, Flat Fee MLS listings are a logical progression of reduced-cost selling alternatives to property owners who are comfortable with managing part or all of the selling process, who believe the MLS will effectively "advertise" their property, and who are willing to pay a buyer's broker a commission.