High-frequency trading (HFT) is a broad term without a precise legal or regulatory definition. It is used to describe what many characterize as a subset of algorithmic trading that involves very rapid placement of orders, in the realm of tiny fractions of a second. Regulators have been scrutinizing HFT practices for years, but public concern about this form of trading intensified following the April 2014 publication of a book by author Michael Lewis. The Federal Bureau of Investigation (FBI), Department of Justice (DOJ), Securities and Exchange Commission (SEC), Commodity Futures Trading Commission (CFTC), the Office of the New York Attorney General, and the Massachusetts Secretary of Commerce have begun HFT-related probes.