The Feedback Closure Principle (FCP) proposes that stability in complex systems emerges from the resolution of constraints through feedback. Disturbances create mismatches between a system’s current state and its viable operating range. Feedback processes act to detect, regulate, and reduce these mismatches. When the constraint is sufficiently resolved, the feedback loop “closes,” restoring system stability or establishing a new adaptive equilibrium. The framework provides a general way to analyse stability, recovery, and regulation across biological, physical, and computational systems.