This paper advances understanding of the materiality concept, application, implications and transposition from the financial reporting/audit to sustainability reporting/assurance contexts. We analyze and compare conceptualizations of materiality in contemporary standards and based on interviews with preparers and auditors. We find transposition from traditional accounting to sustainability is enabled (in both directions) by multidisciplinary sustainability reporting and assurance teams and is an ongoing process. We make theoretical and empirical contributions to prior literature by simultaneously considering materiality in the financial reporting, sustainability reporting, financial audit and sustainability assurance domains, whereas prior literature deals with one or two domains at a time. Theoretically we identify and compare key attributes of the materiality concept and provide empirical data on transposition. We offer preparers and auditors/assurers empirical evidence of the challenges and processes for implementing materiality and our findings support standard setters in developing materiality guidelines.