A real estate broker is a party who acts as an intermediary between sellers and buyers of real estate 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.

In the US, real estate brokers and their salespersons (commonly called real estate agents) assist sellers in marketing their property and selling it for the highest possible price under the best terms. When acting as a Buyers agent with a signed agreement, they assist buyers by helping them purchase property for the best possible price under the best terms. Due to the importance of this role, most brokers that seek to play the role of client advocate are now seeking out the services of Certified Mortgage Planners, industry experts that work in concert with Certified Financial Planners to align consumers' home finance positions with their larger financial portfolio(s). Without an 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. Unlicenced activity is illegal, but buyers and sellers acting as principals in the sale or purchase of real estate are not required to be licenced. In some states, lawyers are allowed to handle real estate sales for compensation without being licenced as brokers or agents.