The present invention provides tumor necrosis factor and apoptosis ligand-related leukocyte-expressed ligand 1 receptor (TALL-1R) polypeptides and nucleic acid molecules encoding the same. The invention also provides selective binding agents, vectors, host cells, and methods for producing TALL-1R polypeptides. The invention further provides pharmaceutical compositions and methods for the diagnosis, treatment, amelioration, and/or prevention of diseases, disorders, and conditions associated with TALL-1R polypeptides.