Here, we demonstrate that adaptor protein STING, but not MyD88, is required for type I IFN-dependent antitumor effects of radiation. Electronic address: radiation-mediated tumor regression depends on type I interferon (IFN) and the adaptive immune response, but several pathways control I IFN induction. Electronic address: 7 Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637, USA The Ludwig Center for Metastasis Research, University of Chicago, Chicago, IL 60637, USA. 6 Department of Pathology, University of Chicago, Chicago, IL 60637, USA The Ludwig Center for Metastasis Research, University of Chicago, Chicago, IL 60637, USA.5 Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.4 Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637, USA.3 Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.2 Department of Pathology, University of Chicago, Chicago, IL 60637, USA.1 Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637, USA The Ludwig Center for Metastasis Research, University of Chicago, Chicago, IL 60637, USA.