This report summarizes the benefits and risks of algorithmic trading in U.S. capital markets as required by Congress. It provides an overview of the structure of equity and debt markets and how algorithms are used in trading. The report finds that algorithmic trading has generally improved market quality and liquidity during normal periods, but may exacerbate volatility during stress. It also notes operational risks from increased complexity and interconnection of markets. The report makes no policy recommendations but provides information for regulators to consider.