The Financial Industry Regulatory Authority, Inc. recently announced that the previously approved rule change relating to the “best execution” obligation of broker-dealers will become effective on May 31, 2012. The Securities and Exchange Commission approved the rule change earlier this year, but FINRA did not announce an effective date at that time. New FINRA Rule 5310 and related Supplementary Material replace current NASD Rule 2320. FINRA Rule 5310 leaves in place the general requirements of NASD Rule 2320, requiring member firms to use “reasonable diligence” in any transaction for or with a customer (or a customer of another broker-dealer) to ascertain the best market for a security to be bought or sold at the price most favorable to that customer under prevailing market conditions. The new rule also includes provisions related to interpositioning (i.e., interjecting a third party between the member and the best available market), the use of a brokerʼs broker, the staffing of order rooms, and the application of the best execution requirements to other parties.