Reasons for failure of the immune system to fight cancer include tumor immune escape mechanisms, limited availability of tumor-specific antigens, and failure to deliver tumor antigens in the right immunological context. Progress in molecular biology and immunology has provided technologies that can detect an ever-widening choice of new tumor-specific antigens. One of the most important questions remains the delivery of these tumor antigens in an effective way to the immune system of a cancer patient. This task is performed in normal circumstances by dendritic cells (DCs). DCs are sentinels of the immune system located at sites of antigen entry such as skin. They take up antigen and carry it to secondary lymphoid organs. They are highly specialized antigen-presenting cells (APCs) for the activation of specific effector T cells recirculating in secondary lymphoid organs. In recent years an enormous increase in our understanding of DC biology has opened up new ways of applying these cells for immunotherapy of cancer.