What is Regulation NMS?

Regulation National Market System is a US financial regulation promulgated and described by the United States Securities and Exchange Commission as "a series of initiatives designed to modernize and strengthen the National Market System for equity securities". The Reg NMS is intended to assure that investors receive the best price executions for their orders by encouraging competition in the marketplace. Some contend that the rule has contributed to the rise of high-frequency trading, which is sometimes regarded as controversial.