This master’s thesis explores the role of the Big 4 and Big 3 in helping corporations navigate the Corporate Sustainability Reporting Directive (CSRD), a key European Union initiative aimed at enhancing transparency in environmental, social, and governance (ESG) practices. The research indicates that these firms function not solely as advisors but also actively shape how companies understand and implement sustainability reporting. They act as knowledge producers and influence both corporate strategy and broader discourse. The study also con-siders how economic conditions and regulatory changes, specifically the EU’s Omnibus package, impacts this landscape, suggesting a potential shift towards reduced reporting re-quirements for fewer companies; however, with a chance for higher quality reporting, this will ultimately also reinforce the market position of larger accounting and consulting firms. The thesis demonstrates the intricate interplay between regulation, consulting services, eco-nomic factors, and the evolving approach to corporate sustainability reporting.