Bitcoin exchange platforms match buyers with sellers. Like a traditional stock exchange, traders can opt to buy and sell bitcoin by inputting either a market order or a limit order. When a market order is selected, the trader is authorizing the exchange to trade his coins for the best available price in the online marketplace. With a limit order set, the trader directs the exchange to trade coins for a price below the current ask or above the current bid, depending on whether s/he is buying or selling.