Marc Isaiah Grossman (born September 23, 1951) is an American former diplomat and government official. He served as United States Ambassador to Turkey, Assistant Secretary of State for European Affairs, and Under Secretary of State for Political Affairs. He was most recently the United States Special Representative for Afghanistan and Pakistan and is currently a Vice Chairman of The Cohen Group, a business consulting and lobbyist firm of former Defense Secretary William Cohen, and a member of the German Marshall Fund board of trustees.