This chapter focuses on dendritic cells (DCs) and discusses the recent progress in DC biology and the potential implications of DCs in the context of immunization against cancer. DCs are professional antigen-presenting cells (APCs), which have the unique ability to induce and sustain immune responses, and they are now recognized as an integral part of the lymphohematopoietic system. DC progenitors in the bone marrow give rise to circulating precursors that home the tissue, where they reside as immature cells with high phagocytic capacity. Upon tissue damage, immature DCs capture antigen (Ag) and subsequently migrate to the lymphoid organs, where they select rare Ag specific T cells, thereby initiating immune responses. DCs present Ag to CD4+ T cells, which in turn regulate other immune effectors, including Ag-specific CD8+ T cells and B cells, as well as non-Ag-specific macrophages, eosinophils, and natural killer (NK) cells. Dendritic cells are crucial players in several immunotherapy approaches either as targets or as vectors for induction of tumor-specific immunity, both in vivo and ex vivo.