Ligation of the Fas (CD95) receptor leads to an apoptotic death signal in T cells, B cells, and macrophages. However, human CD34⁺–derived dendritic cells (DCs) and mouse DCs, regardless of their maturation state, are not susceptible to Fas-induced cell death. This resistance correlates with the constitutive expression of the Fas-associated death domain–like IL-1β–converting enzyme (FLICE)-inhibitory protein (FLIP) ligand. We demonstrate a new role of Fas in DC physiology. Engagement of Fas on immature DCs by Fas ligand (FasL) or by anti-Fas antibodies induces the phenotypical and functional maturation of primary DCs. Fas-activated DCs upregulate the expression of the major histocompatibility complex class II, B7, and DC–lysosome-associated membrane protein (DC-LAMP) molecules and secrete proinflammatory cytokines, in particular interleukin (IL)-1β and tumor necrosis factor α. Mature DCs, if exposed to FasL, produce even higher amounts of IL-1β. Importantly, it is possible to reduce the production of IL-1β and interferon (IFN)-γ during DC–T cell interaction by blocking the coupling of Fas–FasL with a Fas competitor. Finally, during cognate DC–T cell recognition, IL-12 (p70) could not be detected at early or late time points, indicating that Fas-induced, IFN-γ secretion is independent of IL-12.