Alpha-1-antitrypsin deficiency (AATD) is a rare genetic disorder that predisposes for the development of liver and lung disease. AAT is also referred to as alpha1-proteinase inhibitor (a1-PI) and is a 52-kD glycoprotein secreted by the liver into the blood. Agglomeration of the AAT-protein in hepatocytes can result in liver disease. The major function of AAT in the lungs is to protect the connective tissue from attack of the elastase released by triggered neutrophils. Exposure to environmental smoke is the major risk factor for the development of lung disease that manifests as early chronic obstructive lung disease (COPD).AATD is a rare condition (1:5000-10000). As one consequence, data and information on diagnosis and treatment are not easily accessible. This book provides a comprehensive overview on AATD, including information on basic biology, diagnostic strategies, rare manifestations, therapeutic approaches, and patients care structures. The text offers an introduction in many aspects of this rare condition and aims to equip the clinician with the necessary knowledge to adequately care for individuals with AATD.