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. From a market microstructure theory standpoint, market makers are net sellers of an option to be adversely selected at a premium proportional to the trading range at which they are willing to provide liquidity.

Most foreign exchange trading firms are market makers and so are many banks, although not in all currency markets. In foreign exchange (or FX) trading, where most deals are conducted over-the-counter and are, therefore, completely virtual, the market maker sells to and buys from its clients and is compensated by means of price differentials for the service of providing liquidity, reducing transaction costs and facilitating trade. Recent developments in the over-the-counter FX market have permitted even buy-side (non bank participants) virtually to act as market-makers through the advent of high speed/frequency software engines that submit bids and offers outside prices available on other networks or ECN (electronic communication network) where FX is traded.