Multiple myeloma (MM) is a cancer originating from terminally differentiated B lymphocytes, the plasma cells and is classified as a B cell non-Hodgkin lymphoma. As clonal plasma cells secrete immunoglobulin molecules (lacking antigenic specificity), an "M component" can incidentally be detected. Besides intact immunoglobulin molecules, free light chains can be produced. Although there is no specific treatment for monoclonal gammopathy of undetermined significance (MGUS), which is the defined as the presence of clonal bone marrow plasma cells and low levels (serum and/or urine) of the M component, it should be followed up in affected individuals. The symptoms of MM are numerous and often nonspecific. Diagnosis includes the quantification of monoclonal proteins in serum and urine, blood count, electrolytes and renal function, imaging of the skeleton and bone marrow puncture. The cornerstone of therapy includes melphalan- or cyclophosphamide-based regimens incorporating one of the "novel drugs" (i.e. bortezomib, thalidomide, or lenalidomide).