A real estate broker is a term in the United States which describes a party who acts as an intermediary between sellers and buyers of real estate (or real property as it known elsewhere) and attempts to find sellers who wish to sell and buyers who wish to buy. In the United States, the relationship was originally established by reference to the English common law of agency with the broker having a fiduciary relationship with his clients.

Estate agent is the term used in the United Kingdom to describe a person or organization whose business is to market real estate on behalf of clients, but there are significant differences between the actions and liabilities of brokers and estate agents in each country. Beyond the US, other countries take markedly different approaches to the marketing and selling of real property.

In the US, real estate brokers and their salespersons (commonly called "real estate agents" or, in some states, "brokers") assist sellers in marketing their property and selling it for the highest possible price under the best terms. When acting as a Buyer's agent with a signed agreement (or, in many cases, verbal agreement, although a broker may not be legally entitled to his commission unless the agreement is in writing), they assist buyers by helping them purchase property for the lowest possible price under the best terms. Without a signed agreement, brokers may assist buyers in the acquisition of property but still represent the seller and the seller's interests.

In most jurisdictions in the United States, a person is required to have a license in order to receive remuneration for services rendered as a real estate broker. Unlicensed activity is illegal, but buyers and sellers acting as principals in the sale or purchase of real estate are not required to be licensed. In some states, lawyers are allowed to handle real estate sales for compensation without being licensed as brokers or agents.