A stock trader or a stock investor is an individual or firm who buys and sells stocks in the financial markets. Many stock traders will trade bonds (and possibly other financial assets) as well. Trading stocks is a risky and complex occupation because the direction of the markets are generally unpredictable and lack transparency, also financial regulators are sometimes unable to adequately detect, prevent and remediate irregularities committed by malicious listed companies or other financial market participants. In addition, the financial markets are usually subjected to speculation.

Stock traders advise shareholders and help manage portfolios. Traders engage in buying and selling bonds, stocks, futures and shares in hedge funds. A stock trader also conducts extensive research and observation of how financial markets perform.