Radiotherapy is one of the main tumor treatment modalities that provides great survival benefits to patients with cancer. However, it is important to pay attention to the occurrence of adverse events after radiotherapy and take early measures. Radiation pneumonitis (RP) is a major adverse response in patients with cancer receiving thoracic radiotherapy, and it affects the quality of life and survival of patients. We analyzed the latest evidence on RP, and summarized research developments on the pathophysiological mechanism, risk factors, clinical manifestations, diagnosis and differential diagnosis, classification, treatment, and prognosis to form a consensus. With the development of comprehensive treatments, including immunotherapy, the diagnosis and identification of RP has become more complex, requiring multidisciplinary discussion and decision-making. In the future, it is critical to explore more effective treatments, various risk factors, and precautions for RP.