This chapter focuses on the mechanisms that can control or limit opportunistic non-GAAP disclosure, examining both internal and external systems. It addresses the role of corporate governance, board oversight, and internal audit structures in monitoring financial communication practices. It also analyzes the role of external auditors and securities market regulators, with a special focus on ESMA’s Guidelines for Alternative Performance Measures. In fact, empirical findings on European companies reveal a generally low level of compliance with regulatory expectations. The limitations of existing enforcement systems are discussed, setting the stage for the next chapter on standard setters’ interventions on non-GAAP area.