The present invention relates to antibodies and related molecules that immunospecifically bind to B Lymphocyte Stimulator. The present invention also relates to methods and compositions for detecting or diagnosing a disease or disorder associated with aberrant B Lymphocyte Stimulator expression or inappropriate function of B Lymphocyte Stimulator comprising antibodies or fragments or variants thereof or related molecules that immunospecifically bind to B Lymphocyte Stimulator. The present invention further relates to methods and compositions for preventing, treating or ameliorating a disease or disorder associated with aberrant B Lymphocyte Stimulator expression or inappropriate B Lymphocyte Stimulator function comprising administering to an animal an effective amount of one or more antibodies or fragments or variants thereof or related molecules that immunospecifically bind to B Lymphocyte Stimulator.