Hereditary angioedema (HAE) is a rare disorder first described in 1888 by Sir William Osler. Since then, our understanding of this condition has increased tremendously. This article reviews the historical aspects, classification, pathophysiology, clinical presentation, and laboratory diagnosis of HAE. A review was performed of historical and current literature of HAE. HAE I and II are related to insufficient production of C1-esterase inhibitor (C1-INH) or production of a dysfunctional C1-INH protein, respectively. HAE III is not related to C1-INH deficiency and the pathogenesis is unknown. Bradykinin appears to be the main mediator responsible for angioedema in patients with C1-INH deficiencies. Angioedema of the extremities, face, and upper airway along with gastrointestinal angioedema are the most common clinical features in HAE. The laboratory tests that are most commonly used in the diagnosis of HAE include C4, C1-INH concentration, and C1-INH function. Advances in our understanding of the pathogenesis of HAE have led to several advances in the therapy of this disease. Despite our more thorough understanding of the genetics and pathophysiology of HAE, many questions remain unanswered.