Behçet's Disease (BD) is one of the most-studied systemic disorders characterized by an occlusive vasculopathy of multiple organs. The etiology and pathogenesis of BD are still unclear, but there is evidence for genetic, immunologic and infectious factors in the onset and throughout the course of the disease. Immunology of Behçet's Disease highlights various aspects of BD. After an epidemiological overview, the clinical presentation of ocular and non-ocular symptoms of BD are summarized. The immunopathological changes reflect a chronic vasculitis of arterioles, venules and capillaries. The role of T-cells, but also of NK-T-cells, secreted cytokines and neutrophils is covered. For years microorganisms have been under investigation as initiating BD and, in particular, immune reactions against various microbial heat shock proteins could be an important etiological factor. It has been shown that the pathogenic gene involved in the development of BD is pinpointed to HLA-B51. Finally, the treatment of BD is discussed in detail, including new options like anti-TNF-alpha-antibodies and interferon-alpha. Immunology of Behçet's Disease summarizes our knowledge regarding the most important factors that induce or trigger BD and will stimulate research in the field and help to initiate new ideas.