Excessive monoclonal light chain production and excretion may result in a variety of renal diseases which may collectively or individually be referred to as light chain nephropathy. Kappa light chains are more likely to produce tubular dysfunction and nodular nonamyloidotic glomerulosclerosis, while lambda light chains are more likely to be involved in the development of amyloidosis. The physicochemical reasons for this segregation are poorly understood. Affected patients may present with minor tubular dysfunctions, acute or chronic renal failure, mild proteinuria, or severe nephrotic syndrome. Underlying each is a dyscrasia of plasma cells or frank multiple myeloma with excessive production of monoclonal light chains. Electron microscopy and immunofluorescence studies of renal biopsies have been critical in defining these nephropathies and continue to be essential in establishing the diagnosis.