Diabetes in the setting of diseases of the exocrine pancreas has long existed as a known, but underdiagnosed or misdiagnosed, disorder. It currently finds itself in a state of taxonomic dereliction and requires a long overdue refurbishment. Correct conceptualisation is a key precondition for knowledge development in this disorder. This article lays out the epistemiological foundation for diabetes of the exocrine pancreas (DEP) and presents a synthesis of the current interdisciplinary discourse on diagnosing and classifying DEP. The diagnosis of DEP is generally based on the most up-to-date biochemical criteria endorsed by the American Diabetes Association and European Association for the Study of Diabetes. The presence of exocrine pancreatic dysfunction is not considered a mandatory diagnostic criterion for DEP but is rather a significant risk factor for developing DEP. DEP principally comprises post-pancreatitis diabetes mellitus, pancreatic cancer-related diabetes, and cystic fibrosis-related diabetes, which are mutually exclusive with autoimmune diabetes and type 2 diabetes. Other exclusions and stipulations apply. The DEP criteria will be instrumental in aiding optimal design and conduct of clinical studies, uniform collection of health utilisation data, meaningful comparison of scientific findings across countries, and clear communication among stakeholders (healthcare providers, patients, health regulatory authorities, pharmaceutical industry).