Dendritic cells (DCs) are antigen presenting cells with unique capability to take up and process antigens in the peripheral blood and tissues. They subsequently migrate to draining lymph nodes where they present these antigens and stimulate naive T lymphocytes. During their life cycle, DCs go through two maturation stages and are referred to as immature and mature cells, respectively. While immature DCs are very good at capturing antigens, mature DCs are suitably equipped to present antigens to T cells and to initiate an immune response. DCs with different phenotypes serve as sentinels in nearly all tissues including the peripheral blood, where they are continuously exposed to antigens. Very small numbers of activated DCs are extremely efficient at generating immune response against viruses, other pathogens and in experimental models of tumors. Protection against infectious microorganisms and probably against tumors is provided by complex interactions of the innate and adaptive immune systems. For the initiation to occur, pathogens must first be recognized as a "danger". DC possesses specific receptors to detect such danger signals. The unique immune-stimulating properties of DC and the feasibility of manipulating their function arouse much enthusiasm and hold great promise for the treatment of cancer. Early clinical trials showed that DC can induce immune responses in cancer patients. Nonetheless, cancer treatments based on DC administration require further studies that will optimize this promising treatment modality.