A stock market, or (equity market), is a private or public market for the trading of company stock and derivatives of company stock at an agreed price; these are securities listed on a stock exchange as well as those only traded privately.

The size of the world stock market is estimated at about $51 trillion. The world derivatives market has been estimated at about $480 trillion face or nominal value, 12 times the size of the entire world economy. It must be noted though that the value of the derivatives market, because it is stated in terms of notional values, and cannot be directly compared to a stock or a fixed income security, which traditionally refers to an actual value. Many such relatively illiquid securities are valued as marked to model, rather than an actual market price.

The stocks are listed and traded on stock exchanges which are entities a corporation or mutual organization specialized in the business of bringing buyers and sellers of stocks and securities together. The stock market in the United States includes the trading of all securities listed on the NYSE, the NASDAQ, the Amex, as well as on the many regional exchanges, e.g. OTCBB and Pink Sheets. European examples of stock exchanges include the London Stock Exchange, the Deutsche Börse and the Paris Bourse, now part of Euronext.