Multiple myeloma is a hematologic malignancy characterized by abnormal plasma cells in the bone marrow, with potential uncontrolled growth causing destructive bone lesions, kidney injury, anemia, and hypercalcemia. Edward Libby, MD, of the University of Washington, joins JAMA Associate Editor Ethan Basch, MD, of the University of North Carolina, for a discussion of the diagnosis, complications, and management of myeloma, as well as the related conditions of monoclonal gammopathy of undetermined significance (MGUS) and smoldering myeloma. Related Content: Diagnosis and Management of Multiple Myeloma Patient Information: Multiple Myeloma