The 1st Battalion, 503rd Infantry Regiment (1–503rd IR) is an active duty airborne infantry battalion in the United States Army, assigned to the 173rd Airborne Brigade Combat Team and stationed in Vicenza, Italy.

The battalion has served with the 2nd Infantry Division, the 11th Airborne Division, the 24th Infantry Division, the 82nd Airborne Division, and the 173rd Airborne Brigade; has been stationed in Korea, Italy and the United States; and earned campaign credits in World War II, the Vietnam War, Operation Enduring Freedom-Afghanistan, and Operation Iraqi Freedom.

The lineage of Company A, 503rd AIR, was reorganized and redesignated on 1 March 1957 as Headquarters and Headquarters Company, 1st Airborne Battle Group, 503rd Infantry, and remained assigned to the 11th Airborne Division (organic elements concurrently constituted and activated).

Shortly thereafter, on 25 June 1963, it was reorganized and redesignated as the 1st Battalion (Airborne), 503rd Infantry.

Note: The published Army lineage shows War on Terrorism "Campaigns to be determined".