This chapter reviews the current clinical, histologic, and immunologic features of the most common forms of autoimmune bullous diseases. Autoimmune bullous diseases are rare disorders affecting skin and mucous membranes and are mediated by pathogenic autoantibodies against desmosomal or hemidesmosomal antigens of squamous epithelium. In the epidermis, neighboring keratinocytes adhere to each other through organelles known as desmosomes, whereas at the dermoepidermal junction hemidesmosomes anchor the epidermis to the dermis. The majority of these antigens recognized by these autoantibodies are desmosomal and hemidesmosomal transmembrane glycoproteins involved in epidermal cell-cell and epidermal-dermal adherence. The pemphigus syndromes include diseases that are characterized by loss of epidermal cell-cell cohesion and autoantibodies against desmosomal cadherins. This group comprises the two classical forms of pemphigus: pemphigus vulgaris (PV) and pemphigus foliaceus (PF). PV is characterized by suprabasilar acantholysis and anti-Dsg3 IgG autoantibodies, whereas PF is characterized by subcorneal acantholysis and anti-Dsg1 IgG autoantibodies. Other infrequent forms of pemphigus include paraneoplastic pemphigus (PNP), drug-induced pemphigus, and IgA pemphigus are also discussed. © 2006 Elsevier Inc. All rights reserved.