The aim of the EU’s cohesion policy is to reduce development disparities between Member States and regions across the EU and thus increase its economic, social and territorial cohesion. The policy is planned and implemented under shared management by the European Commission and the Member States and their regions. It is characterised by a multi-level governance structure, with numerous actors and stakeholders, and a formal three-level control structure. Since 2007, audit authorities (AAs) in Member States and regions have played a key role as a functionally independent layer of audit, contributing to the Commission’s assurance about the regularity of cohesion spending and the reliability of the performance information reported by Member States. This paper provides an overview of the set-up and responsibilities of AAs, and of how the legislative framework has evolved over the last three programming periods. It also summarises recent European Court of Auditors (ECA) assessments of the work of AAs and their contribution to good governance in cohesion spending. In this context, the article refers also to the specific matter of State aid as one means by which, under restrictive conditions, Member States may support enterprises and thus foster economical and regional development. AAs are at the forefront to verify the compliance of granted aid with European State aid rules that are a key condition for the effective functioning of the European Single Market. Keywords: cohesion policy, cohesion funding, multi-level governance, managing authority, certifying authority, audit authority, assurance package, statement of assurance, State aid compliance