Purpose: Expert review summarizing the overcome tumor cell hypoxia by treatment modification in radiation oncology. Methods: An extensive literature search regarding various means of treatment modification was performed and key papers on those modifications were included in this review article. Results: Based on the identified key papers the means to overcome hypoxia in radiation oncology were summarized in this review article, e.g., increasing levels of oxygen, combining radiotherapy with agents counteracting hypoxia, or modifying radiation treatment itself. Conclusions: This review summarizes the results of preclinical and clinical studies counteracting hypoxia and highlights the measures that have found their way into clinical practice.