Program trading is a type of trading in securities, usually consisting of baskets of fifteen stocks or more that are executed by a computer program simultaneously based on predetermined conditions. Program trading is often used by hedge funds and other institutional investors pursuing index arbitrage or other arbitrage strategies. There are essentially two reasons to use program trading, either because of the desire to trade many stocks simultaneously, or alternatively to arbitrage temporary price discrepancies between related financial instruments, such as between an index and its constituent parts.