Book excerpt: Using illustrative case examples, this book thoroughly reviews similarities and differences between asthma, chronic obstructive pulmonary disease (COPD) and the overlap syndrome. It is important to highlight the distinctions because these commonly encountered conditions in respiratory and primary care share many similarities but have important differences often mistaken for each other. This can have serious implications for treatment, particularly as new treatments are targeted at specific phenotypes of the diseases. This practical guide shows how to distinguish between the diseases on a pathological and clinical basis so that appropriate management and treatment may be pursued.