For decades, the auditing profession has been under scrutiny, due in part to its close association with a business rationale. This has led to some to call for de-professionalization, where accountability, control, and commerce would threaten auditing’s autonomy. Yet auditing is regarded as a principle of social organization and control, wherein it produces trust and legitimacy to society. By focusing on the individual auditor and the micro-level dynamics in the auditor’s organizational context, this dissertation challenges traditional notions of professionalism and commercialism as dichotomies. Based on documents, observations, and in-depth interviews with auditors holding different levels of experience, performance was targeted as a central concept for auditors’ understanding of auditing as a social and organizational phenomenon. Accordingly, by critically appraising the significance of performance in the professional-organizational context of Big Four firms, this dissertation engages with auditors’ reasoning and everyday work activities. Here, performance is suggested to hold a central role in how auditors manage and reconcile conflicting institutional logics — as well as accountability demands — in their everyday work. By theorizing on the mediating role of performance, this dissertation explores how performance is enacted in both structure (control, rituals and norms) and agency (reflexive monitoring and rationalization). Drawing on structuration theory, performance is shown to constitute modalities in actors’ use of structure, a process in which conflicting institutional logics are replicated, revised, and rejected. The findings further pinpoint the active role of auditors in mobilizing and defining legitimate performances within particular local settings. In this, a previously neglected interplay between bureaucratic and social performance practices that is performed by auditors is recognized as essential in exploring auditing as defined in the local professional-organizational settings. This interplay suggests a need to further attend how auditing is performed by practitioners in micro-level, everyday work. To conclude, this dissertation indicates that auditors’ reasoning on and mobilization of performance define the evolving auditing profession, one where rules and accountability regimes dominate. As a consequence, the influence of individual agency, professional communities, and social interaction are emphasized as key components for our understanding of the continuously developing professional field of auditing and the maintenance of a strong professional ethos.