Autoimmune blistering skin diseases are characterized by autoantibodies to structural components of the skin. Diagnosis is based on the detection of autoantibodies in the skin and/or serum of the patients. Tissue-bound autoantibodies are found by direct immunofluorescence microscopy of tissue-bound autoantibodies and are still considered the gold standard for the diagnosis of autoimmune bullous diseases. Circulating antibodies are first characterized by indirect immunofluorescence microscopy on organ sections including monkey esophagus and 1M NaCl-split human skin. Specificities of these circulating autoantibodies are then analyzed by immunoblotting, ELISA, or immunoprecipitation. More recently, ELISA-based detection systems for some of these autoantibodies have become commercially available. Frequently, the levels of circulating autoantibodies as detected by ELISA correlate with disease activity and facilitate the evaluation for further need of treatment. In cases where the clinical picture strongly suggests an autoimmune bullous disease, diagnosis may be based only on serological tests. This review summarizes the diagnostic steps in the different autoimmune bullous skin diseases.