The Mexican Border Service Medal or Mexican Border Defense Medal was a U.S. service medal established by an Act of Congress on July 9, 1918. It was initially awarded for service on the border between May 9, 1916 and March 24, 1917. Additionally, recipients included those who performed duty with the Mexican Border Patrol between January 1, 1916 and April 6, 1917. This should not be confused with the Mexican Border Defense Medal (MBDM), a different service medal authorized in 2025 for service on the Mexico-United States border bearing the same design.