Market making is a trading strategy where a market maker, which can be an individual or a firm, provides liquidity to a market by buying and selling securities for its own account. The market maker quotes both a buy and a sell price in a tradable asset held in inventory, hoping to make a profit on the bid-ask spread, or turn. Market makers provide liquidity and depth to markets and profit from the difference in the bid-ask spread. They also make trades for their own accounts, which are known as principal trades. Market makers participate in the market at all times, buying securities from sellers and selling securities to buyers. They display buy and sell quotations for a guaranteed number of shares and immediately sell from their own holdings or inventory of those shares to complete the order. The income of a market maker is the difference between the bid price, the price at which the firm is willing to buy a stock, and the ask price, the price at which the firm is willing to sell it. Market making is aimed at infusing liquidity and is mostly a market-neutral trading strategy used for securities traded on exchanges. Market makers can either be individuals or broker-dealers who meet a certain set of requirements around education, training, capital adequacy, and so on.