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The immune system plays an important role in both the initiation and development of head and neck cancers. Various immune checkpoints have been discovered that are used by cancer cells to escape the immune response. In this context, inhibitor antibodies against immune checkpoints, also referred to as immunotherapy, have been developed to combat immune escape by tumor cells and are currently used to treat recurrent and/or metastatic head and neck cancers (anti-PD-1 antibodies). In addition, the immune system appears to play an important role in the response to radiotherapy. Although anti-tumoral efficacy of radiotherapy is largely based on DNA toxicity, studies have suggested that this efficacy depends not only on this cytotoxic and local antiproliferative effect, but also on changes in interactions between the tumor and its microenvironment. The cytotoxic action of radiotherapy on tumor cells delivers tumoral neoantigens to T lymphocytes and releases pro-inflammatory cytokines, which encourage the immune response. Cell death that induces this type of immune response is known as immunogenic death. In this context, the combination of immunotherapy and radiotherapy has raised much hope for improving the anti-tumor response of the immune system, and several clinical trials have been launched. In this article, we present a literature review highlighting the importance of the immune system in head and neck cancers, the justification of combining radiotherapy and immunotherapy, the main clinical trials involving radiotherapy and immunotherapy, as well as some hypotheses based on the mixed results of these trials.