A recent workshop on "Dendritic Cells: Biology and Therapeutic Applications," sponsored by the Juan March Foundation, brought together basic and clinical research scientists to discuss the mechanisms underlying the control of immune responses and tolerance by dendritic cells (DCs), as well as recent research in cancer immunotherapy based on DC vaccination. Particular emphasis was placed on antigen processing and presentation by DCs, C-type lectin antigen receptors, DC maturation and polarization of T cell responses, the control of immunity versus tolerance by DCs, the developmental origin of DCs, and the use of DCs in cancer immunotherapy.