The Hollywood Stock Exchange, or HSX, is a web-based, multiplayer game in which players use simulated money to buy and sell "shares" of actors, directors, upcoming films, and film-related options.

Because trading directly affects the prices of the securities — purchasing enough shares of a stock causes its price to rise, and selling causes its price to fall — and because the ultimate value of a moviestock is based on the film's box office, stock prices act as box office predictions. For example, if a particular moviestock trades at "H$40.00", the market is predicting that the movie will gross US$40 million at the box office in the first four weeks of release. In 2002, players in the Hollywood Stock Exchange correctly predicted 35 of the 40 major-category Oscar nominees. It is considered a good example of a prediction market.

Previous incarnations of the game included a music market (for purchasing musical artists), prizes for top gainers, and, briefly, a "buyout" program in which HSX would reward top players by purchasing their portfolios at a price of US$1.00 per HS1 million if the player would list the portfolio for sale on eBay. These features have been discontinued.