In the last 5 years, numerous studies have been devoted to the biology of multiple myeloma (MM) and of the monoclonal plasma cell process termed monoclonal gammopathy of undetermined significance (MGUS). Presenting features of MM are changing, with a shift from symptomatic to indolent or localized presentations. Post-MGUS MM are frequent. There is now striking evidence that myeloma cells have an abnormal biology, especially an aberrant differentiation and survival pathway inside the bone marrow. Their aberrant phenotype and genotype are probably responsible for this. Several studies have emphasized the essential role of interleukin-6 (IL-6) as a survival and growth factor for myeloma cells and the interest in anti-IL-6 therapy in MM.