Regulation NMS (2005)
The Securities and Exchange Commission adopted Regulation NMS, including Rule 611, which requires trading centers to avoid trading through protected quotes on exchanges. The rule made displayed exchange quotes legally special and set the terms for how off-exchange venues interact with lit markets.
Exchanges and electronic venues rebuilt their routing systems around the rule.
Alternative trading systems grew into a large share of U.S. equity volume under that framework.
The SEC is now considering rescinding Rule 611, which would change the value of both exchange status and ATS distribution.
