"High-frequency trading (HFT) generally refers to trading in financial instruments, such as securities and derivatives, transacted through supercomputers executing trades within microseconds or milliseconds (or, in the technical jargon, with extremely low latency). There is no universal or legal definition of HFT, however. Neither the Securities and Exchange Commission (SEC), which oversees securities markets, nor the Commodity Futures Trading Commission (CFTC), which regulates most derivatives trading, have specifically defined the term. By most accounts, high frequency trading has grown substantially over the past 10 years: estimates hold that it accounts for roughly 55% of trading volume in U.S. equity markets and about 40% in European equity markets. Likewise, HFT has grown in futures markets--to roughly 80% of foreign exchange futures volume and two-thirds of both interest rate futures and Treasury 10-year futures volumes. […] This report provides background on various HFT strategies and some associated policy issues, recent regulatory developments and selected enforcement actions by the SEC and CFTC on HFT, and congressional action such as proposed legislation and hearings related to HFT."
CRS Report for Congress, R44443
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html