Ku and Diehl’s chapter broadens the traditional conception of secondary rules, defining the international legal system as composed of operating and normative subsystems respectively. Three sets of mechanisms by which secondary rules influence primary rules are examined: (1) configuring institutional frameworks, (2) enhancing the credible commitment of new primary rules, and (3) institutions directly or indirectly making normative law. The conclusions are that secondary rules play important roles in each of these areas. A consistent theme is that the operating system can reduce uncertainty and fill gaps in the existing governance structures. There, secondary rules promote efficiency and coherence in the law. There are, however, instances in which such rules complicate matters, as in several cases lawmaking might be stifled and governance not promoted.