The factors that have contributed to the adoption of high-speed trading and affected market structure in recent years include competition, technology, and regulation. The unexpected ways in which these dynamic forces are coming together raise a number of important policy issues.

A handful of high-frequency trading firms accounted for an estimated 70 percent of overall trading volume on U.S. equities markets in 2009. One firm with such a computerized system traded over 2 billion shares in a single day in October 2008, amounting to over 10 percent of U.S. equities trading...

A small group of high-frequency algorithmic trading firms have invested heavily in technology to leverage the nexus of high-speed communications, mathematical advances, trading and high-speed computing. By doing so, they are able to complete trades at lightning speeds. High-frequency algorithmic...