Radiation therapy plays a critical role in the management of a wide range of hematologic malignancies. The optimal radiation dose and target volume, and safe and effective ways of integrating radiation with systemic agents, vary depending on the histologic subtypes, stage at presentation, patient performance status, response to systemic therapy if given, treatment intent, and patient preferences. Limiting doses to surrounding organs without sacrificing disease control is of paramount importance. Reducing radiation doses and treatment volume in selected cases, and the use of advanced radiotherapy technology, can improve the therapeutic ratio of patients receiving radiation therapy for hematologic malignancies.