Radiotherapy not only allows us to selectively target the tumour, it also interacts with the tumor microenvironment and consequently the host’s immune system. Theoretically this can lead to an in situ vaccination and trigger so-called abscopal responses, away from the irradiated site. Unfortunately, these are rarely seen the clinic. Over the past years, both preclinical and clinical studies demonstrated synergistic effects of radiation in combination with several types of immunotherapy. However, the optimal dose and fractionation of radiation therapy as well as the optimal combination and sequence of radiotherapy and immunotherapy still needs to be determined.