Marc Isaiah Grossman 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 strategic advisory firm headed by former U.S. Secretary of Defense William Cohen, and a Vice Chair of the German Marshall Fund board of trustees.

The Under Secretary for Political Affairs is currently the fourth-ranking position in the United States Department of State, after the secretary, the deputy secretary, and the deputy secretary of state for management and resources. The current acting under secretary is John R. Bass, who assumed the position following the resignation of Victoria Nuland.