The assumption that a general thermonuclear war is extremely unlikely is held in common by most of the critics of our defense policy as well as by its proponents. Because of its crucial role in the Western strategy of defense, the stability of the thermonuclear balance which, it is generally supposed, would make aggression irrational or even insane is examined. The balance is believed to be precarious, with critical implications for policy. Deterrence in the 1960s will be neither inevitable nor impossible but the product of sustained intelligent effort, attainable only by continuing hard choice. As a major illustration important both for defense and foreign policy, the particularly stringent conditions for deterrence which affect forces based close to the enemy, whether they are U. S. forces or those of our allies, under single or joint control are discussed. Also considered are the inadequacy as well as the necessity of deterrence, the problem of accidental outbreak of war, and disarmament.