 He has served and continues to serve on the council of the American Law Institute, and also has served on the governing boards of the American Philosophical Society, the American Arbitration Association, and the U.S. Supreme Court Historical Society.Since his retirement on February 28, 1992, McKusick has served "of counsel" to Pierce Atwood.In July 1992, he served on a pro bono basis as the neutral arbitrator for the determination of the terms under which Long Island would separate from the City of Portland.