In this paper, we demonstrate and analyze the substance of the added value effect of a Supreme Audit Institution (SAI), focusing on sustainable development issues.We intend to answer such questions as: how could a SAI respond to global and local challenges and how it could help government to implement commitments towards sustainability. Finally, we trace a possible way to improve external audit functions both on the state level and at the International Organization of Supreme Audit Institutions (INTOSAI), by using some ideas from network theory.