Hereditary angioedema (HAE) is a rare autosomal dominant disorder affecting approximately 1 in 50000 persons. It causes frequent attacks of non-pitting, non-pruritic edema without urticaria, usually of the skin of the extremities, gastrointestinal tract, and upper airways. Gastrointestinal attacks may cause severe pain, and attacks in the laryngeal region may lead to asphyxiation and death. HAE usually begins in childhood or adolescence and persists throughout life. The majority of HAE cases are caused by mutations that result in low levels of functional C1-inhibitor (C1-INH), a serine protease inhibitor that plays regulatory roles in the contact, complement, and fibrinolytic systems. Low C1-INH function results in overproduction of bradykinin, the primary cause of HAE symptoms. Type I HAE is characterized by low levels of functional C1-INH, whereas type II HAE is characterized by normal levels of dysfunctional C1-INH. A third type of HAE has a similar presentation, but is not due to C1-INH deficiency or impairment. Some patients with type III HAE carry mutations in the coagulation factor XII gene that do not alter factor XII plasma levels but markedly increase its activity. HAE is often undiagnosed or misdiagnosed, sometimes leading to inappropriate treatment that may include surgery. HAE should be suspected in any patient who presents with repeated attacks of cutaneous edema without urticaria or recurrent unexplained abdominal pain. Diagnosis requires laboratory testing of complement levels. HAE requires disease-specific treatment with agents that increase functional C1-INH levels and/or reduce the production or activity of bradykinin. These treatments include C1-INH concentrates, icatibant, ecallantide, and attenuated androgens. HAE severely reduces patients' quality of life, which makes supportive care an essential part of the treatment program.