Alpha-1 antitrypsin (AAT) is the most abundant proteinase inhibitor within the circulation and AAT deficiency is a genetic disorder characterised by serum levels of less than 11μmol/L. The Z mutation is the most common AAT allele associated with the disease and causes the most severe plasma deficiency, as the mutant protein polymerizes and accumulates within the endoplasmic reticulum of hepatocytes. The retained polymers are associated with cirrhosis and reduced serum levels of AAT contribute to the development of chronic pulmonary disease in AAT deficient individuals. This article will review the importance of AAT as a serine anti-protease, the clinical manifestations of AAT deficiency and specific treatment of the disease. Current therapies including AAT replacement and treatment with synthetic or alternative protease inhibitors are reviewed, along with possible future therapies including those focusing on targeting AAT polymer formation or based on gene therapy.