This study considered the nature of “general principles of law” in the international legal system. While much is known about treaties and customary law, there is a tendency to overlook foundational theoretical questions about general principles in international law. What kind of norms are they? How do they come into existence? What functions do they perform? Focusing on such questions, this study presents a theory of general principles as a distinct category of rules that provides international law with many of its fundamental systemic elements.