An institutional approach to sustainable operations and procurement by third sector organizations SummaryAwareness of (un)sustainable operations is increasing in both academic research and practice.However, little is known about sustainable operations within the third sector. When it comes to sustainable practices, the role played by third sector organizations, and especially non-governmental organizations, has mostly been regarded as advocacy. We shift this traditional perspective by analyzing sustainability of internal operations, including procurement, by third sector organizations.Institutional theory is used to discuss the reporting trends that were found in a document analysis of reports by third sector organizations. We present research lines that might allow understanding drivers and constraints of such (reporting) practices.