Objective: To facilitate distinction between asthma and chronic obstructive pulmonary disease (COPD) in day-to-day primary care practice, and provide practical treatment strategies using spirometric cases to outline how to recognize the clinical and spirometric overlap between asthma and COPD. Sources of information The approaches described here were developed using evidence-based guidelines and the expertise of the authors, including research findings by the authors in the areas of asthma, COPD management, and spirometric testing in primary care. Main message There are patients with clinical or spirometric features of both asthma and COPD. Both asthma and COPD are associated with some degree of inflammation of the respiratory tract, mediated by the increased expression of inflammatory proteins. However, there are clear differences between asthma and COPD in the pattern of inflammation that occurs in the lungs. Diagnostic confusion between COPD and asthma is most likely to arise in older patients with respiratory complaints, particularly against a background that includes cigarette smoke or workplace exposure. Both asthma and COPD are clinical diagnoses based on patient history, symptoms, physical examination findings, and objective measures of lung function. Postbronchodilator spirometry is always needed to confirm a new diagnosis of COPD and should also be performed prebronchodilator for the diagnosis of asthma. However, in many cases, the interpretation of spirometry results is not straightforward. Conclusion Understanding the nature and extent of the spirometric overlap between asthma and COPD is critical for tailoring a therapeutic strategy that is based on factors that include medical and family history, signs and symptoms, and a clear interpretation of spirometry data. This information will be leveraged differently for individual patients to arrive at the correct clinical diagnosis and to select the most appropriate therapy.