Assurance—an intermediary’s guarantee of compliance with regulatory standards—is critical for legitimate governance within the sustainability field. This legitimacy classically depends on the degrees of separation that are needed between the RIT roles to create trust in regulators and enforce the compliance of targets. Following the emergence of the ISEAL Alliance—an apex organization of sustainability standards-setters—there has been a general shift in the sustainability field whereby standard-setters have delegated some of their authority to certifiers and accreditors. This article examines this movement, through the analysis of four different models of assurance, and reveals increasing complexity being built into private systems of regulation in the sustainability field. There is an increasing incidence of multiple actors who engage in processes of intermediation and accreditation, which is rising in importance. The result is empirical and conceptual confusion around previously sacred notions such as independence and conflict of interest as measures of regulatory effectiveness.