Alpha-1 antitrypsin (AAT) deficiency is a common but under-recognized disease. This hereditary disorder is characterized by low levels of AAT, and increased risks of panacinar emphysema at an early age, liver disease, vasculitis and panniculitis. Destruction of lung parenchyma and consequent emphysema result from an imbalance between different inflammatory proteases (in particular, leukocyte elastase), and the major natural antiprotease, AAT. To offer a review of key aspects of this important condition, we present the epidemiology, natural history, and pathogenesis of AAT deficiency and, in the context of recent data and the publication of an international standards document regarding the diagnosis and management of individuals with AAT deficiency, review current therapy of AAT deficiency.