There are different meanings and functions of what is called a “general principle of law.” This article seeks to address their importance as the basis for the systemic integration of the international legal order. When international law is considered as a legal system, its normative unity and completeness seems essential. This article argues that general principles of law are a necessary, although less visible, element of international legal practice and reasoning, which secure the systemic integration and long-lasting underpinnings of international law. In this sense they may be seen as the gentle guardians of international law as a legal system.