Neorealist theories help explain alliance formation and longevity but have trouble explaining why the North Atlantic Treaty Organization (NATO) continues to exist after the cold war. Organizational theories further our understanding by noting that organizations have strong survival instincts, yet NATO survives only as long as its members wish it to. To understand NATO's persistence after the cold war, we must turn to international institutionalist theories to explain why, contrary to neorealist expectations, NATO remains the key international security institution for its members. International institutionalist theories add the conception of NATO as part of a broad multilevel and multi-issue relationship among member states, and this broader context is necessary to explain NATO's persistence.