Radiation therapy (RT) remains a major component of the successful treatment of Hodgkin lymphoma (HL), even in the era of improved systemic therapies. For decades, definitive radiation was used alone to cure the majority of patients with HL, and it is still the most effective single agent in the oncologic armamentarium for this disease. RT as a single modality remains the treatment of choice for patients with early-stage lymphocyte-predominant HL (LPHL) and for a subset of patients with classic HL who have contraindications to chemotherapy. Currently, most patients with HL are treated with combined-modality programs in which RT is given as consolidation after chemotherapy. As the role of RT has transformed over the years from a single modality into an important component of combined-modality therapy, the classic principles of RT fields, dose, and technique have fundamentally changed.