Radiation therapy is emerging as a beneficial and increasingly accessible treatment option for companion animals with cancer. Various types of radiation are available with different properties that may make one more suitable than another for treating a specific tumor type. Radiation therapy can be used as the sole treatment or as part of a multimodality treatment course to result in local or locoregional tumor control, or as palliative therapy for pain control. When radiation is a potential treatment option, it should be considered early in the decision-making process to ensure that the appropriate diagnostics and other treatment modalities are considered to provide the best potential outcome. This article is intended to provide an overview of the types of radiation therapy that are available, the indications, and the potential acute and late radiation side effects.