Celli et al offer an updated definition and severity classification of chronic obstructive pulmonary disease exacerbation (ECOPDs). They propose an updated definition and severity classification of ECOPDs based on the principles outlined by J. Scadding for the taxonomy of diseases, integrating symptoms, function, and surrogate markers of the process underlying ECOPDs. It intends to be objective, practical, and useful to clinicians and researchers alike. In its development, the authors acknowledge that episodes of the worsening of respiratory symptoms similar to ECOPDs may occur in patients with chronic diseases other than COPD, and these potential causes should be considered in the differential diagnosis of the event. The process itself was aided by a medical writer, who identified experts with international recognition who have conducted research and published on the definition, diagnosis, pathobiology, and/or treatment of ECOPDs as well as similar events in closely related fields.