Despite technical improvements concerning lung irradiation modalities, radiation-induced pneumonitis remains a usual complication, notably in the field of lung cancer treatment. This complication may remain asymptomatic but can also lead to respiratory distress. Thus, a low degree of suspicion and a comprehensive work-up is mandatory to evaluate the indication for specific treatment. In this article, we discuss the hypothesized pathophysiologic pathways, risk factors, clinical/radiological presentation and management.