The objective of this paper is to examine the professionalism and professionalization of sustainability assurance providers based on the experiences and perceptions of auditors involved in this activity. This empirical study, based on 38 semi-directed interviews conducted with assurance providers from accounting and consulting firms, shows how practitioners in this area construct and legitimize their professional activity in terms of identity, standardization, and competences. The findings highlight the division of this professional activity between accounting and consulting firms, each of which question the professionalism of the other. The main standards in this area tend to be used as legitimizing tools to enhance the credibility of the assurance process rather than effective guidelines to improve the quality of the verification process. Finally, the complex and multifaceted skills required to conduct sound sustainability assurance and the virtual absence of recognized and substantial training programs in this area undermine the professionalization of assurance providers. This study contributes to the literatures on the assurance of sustainability reports, self-regulation through standardization, and professionalization. It also has important practical implications for standardization bodies, assurance providers, and stakeholders concerned by the quality and the reliability of sustainability disclosure.
