National Command Authority (NCA) is a term used by the United States military and United States government to refer to the ultimate lawful source of military orders. The term refers collectively to the President of the United States (as commander-in-chief) and the United States Secretary of Defense.

The use of the term dates from the Cold War, when the United States and Soviet Union both had nuclear missiles on constant alert and a responsible official had to be available to authorize a retaliatory strike within a matter of minutes. Detailed Continuity of Operations Plans provided for monitoring the whereabouts of certain key government officials who would assume the National Command Authority if the President were killed in an enemy attack.

Only the NCA can order the use of nuclear weapons, including the Single Integrated Operational Plan (SIOP). Neither individual can unilaterally order that strategic nuclear weapons be used; if the NCA determines that a nuclear strike is necessary, they must jointly inform the Chairman of the Joint Chiefs of Staff, who in turn will direct a general officer on duty in the National Military Command Center (NMCC) at the The Pentagon to execute the SIOP.

The term also refers to communications with the commanding officers of the Unified Combatant Commands to put U.S. forces into action.