Monoclonal immunoglobulins and free immunoglobulin light chains are produced by plasma cells as a result of their clonal expansion in plasma cell dyscrasia. These proteins are pivotal in the development of pathologic and clinical symptoms of plasma cell dyscrasia and renal manifestations are frequently the presenting and leading features of this process. The spectrum of pathology associated with monoclonal light chains includes light-chain cast nephropathy and tissue deposits derived from the monoclonal light chain, ie, amyloid derived from the light chains and nonamyloidotic light chain deposition disease. The main diagnostic features, differential diagnosis, and pathogenesis are briefly reviewed.