Radiation therapy is a widely used treatment for locally advanced non-small cell lung cancer, as well as for a variety of other thoracic malignancies. Radiation induced lung injury (RILI) refers to any lung-related change resulting from this treatment. From a clinical standpoint, RILI is separated into two distinct syndromes: an acute pneumonitis beginning 2-10 weeks following RT and a more indolent fibrotic process, presenting months after initial exposure. A variety of factors have been identified that are associated with an increased risk of developing clinically significant RILI. These include treatment-related factors (dose and schedule of radiation, volume of lung irradiated, concurrent use of chemotherapy) and patient-related factors (age, gender, smoking status, presence of pre-existing lung disease). New insights into the mechanisms of radiation induced lung injury have been uncovered, and these findings have led to the development of novel strategies for the prevention and treatment of this complication. In this review, we will discuss the clinical manifestations and risk factors of RILI, and focus on recent advances in its pathogenesis and treatment.