Potential paths to nuclear war and the available means of prevention of nuclear war are discussed. Presented is a detailed description of six nuclear war scenarios, and brief examples of types of potential deterrents to nuclear war (firebreaks) which are relevant for each. To be effective, the right combination of firebreaks must be used, the timing must be correct, and constant re-examination is necessary to insure that the best resources available are being utilized. Scenarios that might culminate in an all-out nuclear war include escalation in a European conflict, in a third world conflict, after a false alarm, after terrorist use of nuclear weapons, and after accidental or unauthorized use of nuclear weapons. Tools, or types of potential firebreaks, that might be employed to prevent the scenarios from starting in the first place, or once started, from escalating to higher and higher levels and eventually reaching general nuclear war fall into the following categories: improved relations; arms control; nuclear nonproliferation; conflict resolution; and crisis of communications. (RM)