This Practice Note discusses Rule 13h-1 under the Exchange Act, including its requirement that large traders engaging in a substantial amount of trading activity in exchange-traded securities register with the SEC on Form 13H, the process of registration under the rule and the obligations of broker-dealers to maintain certain records of large traders effecting transactions using broker-dealers. It also discusses the requirement for broker-dealers to report information on these trading activities when requested by the SEC and to monitor the trading activities of customers to identify large traders that have not registered with the SEC.