In engineering, a fail-safe is a design feature or practice that, in the event of a failure of the design feature, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. Unlike inherent safety to a particular hazard, a system being "fail-safe" does not mean that failure is impossible or improbable, but rather that the system's design prevents or mitigates unsafe consequences of the system's failure. That is, if and when a "fail-safe" system fails, it remains at least as safe as it was before the failure. Since many types of failure are possible, failure mode and effects analysis is used to examine failure situations and recommend safety design and procedures.

Fail-Safe is a bestselling American novel by Eugene Burdick and Harvey Wheeler. Expanded from Wheeler's short story "Abraham '59", it was initially serialized in three installments in the Saturday Evening Post on October 13, 20, and 27, 1962, during the Cuban Missile Crisis.