Mutual assured destruction (MAD) is a doctrine of military strategy and national security policy which posits that a full-scale use of nuclear weapons by an attacker on a nuclear-armed defender with second-strike capabilities would cause the complete annihilation of both the attacker and the defender. It is based on the theory of rational deterrence, which holds that the threat of using strong weapons against the enemy prevents the enemy's use of those same weapons. The strategy is a form of Nash equilibrium in which, once armed, neither side has any incentive to initiate a conflict or to disarm.

The term "mutual assured destruction", commonly abbreviated "MAD", was coined by Donald Brennan, a strategist working in Herman Kahn's Hudson Institute in 1962. However, Brennan came up with this acronym ironically, spelling out the English word "mad" to argue that holding weapons capable of destroying society was irrational.