Since the first American Thoracic Society statement regarding the diagnosis and management of severe alpha-1 antitrypsin (AAT) deficiency in 1989 (1) and the initial Canadian Thoracic Society standards statement in 1992 (2) (which was updated in 2001) (3), significant advances in understanding the cell and molecular biology of AAT and the diagnosis, natural history, and treatment of individuals withAATdeficiency have occurred. These new developments, including completion of several large, longitudinal studies in both Europe and North America and a small randomized controlled trial of augmentation therapy, have provided important new insights that have impacted the clinical management of individuals with severe deficiency of AAT. In the context of these new developments, a need was felt to reexamine recommendations for optimal management of AAT deficiency, to synthesize current knowledge of diagnosis and management for practicing clinicians, and to identify key remaining questions in need of further investigation. With these purposes in mind, a Task Force to develop a new standards document regarding the diagnosis and management of individuals with severe AAT deficiency was formed in 1998 under the auspices of the American Thoracic Society and the European Respiratory Society, with additional sponsorship and support by the Alpha-1 Foundation, the American College of Chest Physicians, and the American Association for Respiratory Care. Under a contractual arrangement, the Veterans Administration Technology Assessment Program, Office of Patient Care Services, Veterans Health Administration provided education regarding preparing an evidence-based document and support in conducting literature searches. In keeping with current standards for developing evidencebased recommendations for optimal care, the current Task Force has undertaken a systematic review of current literature regarding AAT deficiency. Every effort was made to identify the scientific evidence for positions taken and to identify where there was little or no evidence. In the absence of ratable evidence, consensus among members of the Task Force determined the recommendation. This summary document briefly describes the organization and preparation of the Task Force’s report and provides an executive summary of key clinical recommendations. The three following sections are the full systematic reviews prepared by the three individual writing groups that comprised the AAT Deficiency Task Force.