Dendritic cells are the most potent antigen-presenting cells. They, only, can prime naive T lymphocytes. They can also elicit generation of cytotoxic T lymphocytes against viral or tumour antigens and regulate humoral immune responses. The current paradigm is that dendritic cells differentiate from bone marrow progenitors and migrate via the blood to be distributed to tissues ; these immature dendritic cells have the capacity to capture and process antigens ; they then transit through the lymph or blood to lymphoid organs, where they become mature and induce the antigen-specific immune response of T helper cells. Recently developed methods to generate dendritic cells in vitro, have led to better characterization of dendritic cells and to more precislely understand their functions. This has also led to reconsider the « classical » scheme of dendritic cells differentiation, by showing that cells with typical characteristics of dendritic cells may be generated from several differentiation pathways. Presently, dendritic cells have aroused great interest if only because they represent a powerful tool to elicit or to augment, ex vivo, a deficient immune response against tumours or viral infections.