Stephen Gassman's many professional affiliations reflect his longtime leadership in matrimonial law. For starters, he is one of fewer than 100 attorneys in the nation named to the American College of Family Trial Lawyers. He is a Fellow of the American Academy of Matrimonial Lawyers, New York Chapter, a past vice president and the current counsel. He is a past president of the Nassau County Bar Association and a past chair of the Family Law Section of the New York State Bar Association. He is a frequent lecturer at matrimonial law seminars and symposiums conducted by the New York State Bar Association, American Academy of Matrimonial Lawyers, "New York Law Journal," American Bar Association and other prestigious bar groups.