A market maker is a company, or an individual, that quotes both a buy and a sell price in a financial instrument or commodity held in inventory, hoping to make a profit on the bid/offer spread, or turn.

In the United States, the New York Stock Exchange (NYSE) and American Stock Exchange (AMEX), among others, have Designated Market Makers, formerly known as specialists, who act as the official market maker for a given security. The market makers provide a required amount of liquidity to the security's market, and take the other side of trades when there are short-term buy-and-sell-side imbalances in customer orders. This helps prevent excess volatility, and in return, the specialist is granted various informational and trade execution advantages.