Exacerbations of chronic obstructive pulmonary disease (COPD) offer a considerable clinical challenge for clinical practice and drug development. The underlying pathobiology of these characteristic events is unclear. We are far behind other disease areas, such as cardiology, where there are effective approaches for diagnosing and managing acute and potentially fatal events. A joint initiative has begun between the pharmaceutical industry, academia, and the Food and Drug Administration to produce a valid diary card measure of exacerbation severity: the EXAcerbations of Chronic pulmonary disease Test-Patient-Reported Outcome (EXACT-PRO). This article describes the background to this initiative, using the consensus definition of a COPD exacerbation as the starting point from which to propose a new method for quantifying the severity of the event. This approach takes into account the relationships between the symptoms that make up an exacerbation and shows that they can be used in a single continuous severity scale. Methods for defining exacerbation onset and cessation are also proposed.