Bullous pemphigoid, the most common autoimmune blistering disease, is induced by autoantibodies against type XVII collagen. Passive transfer of IgG or IgE antibodies against type XVII collagen into animals has revealed not only the pathogenicity of these antibodies but also the subsequent immune responses, including complement activation, mast cell degranulation, and infiltration of neutrophils and/or eosinophils. In vitro studies on ectodomain shedding of type XVII collagen have also provided basic knowledge on the development of bullous pemphigoid. The pathogenic role of autoreactive CD4+ T lymphocytes in the development of the pathogenic autoantibodies to type XVII collagen should also be noted.