The strides achieved by immunohistochemical techniques, the development of monoclonal antibodies and, more recently, molecular biology have brought deep changes in the concept of histogenesis and in the classification of malignant lymphomas. After blockage, each of the cells which mark out the transformation of B and T may give birth to a malignant lymphoma. In most cases lymphoproliferations retain the immunological (differentiation markers) and morphological attributes of the normal cells from which they derive. It is on this corpus of data that the present histogenesis and classifications are resting. However, the complexity of lymphoma histogenesis is related to heterogeneous lymphoid populations which are not a mere division into B and T cells. There are numerous and not yet clearly individualized subpopulations the morphological and antigenic features of which are imperfectly known. On the other hand, the development of in situ hybridization techniques and of molecular biology (PCR) has provided useful data on the aetiology of malignant lymphomas. The latest results obtained suggest that several viruses (Epstein-Barr, HTLV-1, HHV-6) might play a predominant oncogenic role.