Radiation therapy is used frequently in the treatment of female pelvic malignancies, including gynecologic, colorectal, and urologic cancers to help improve local control and/or survival. Radiation to the pelvis can be delivered using external beam and/or brachytherapy techniques and can be used in several different settings, often in combination with pelvic surgery. The most common uses of radiation include (1) Definitive treatment of cancer (e.g., locally advanced cervical cancer, medically inoperable endometrial cancer, rectal cancer in the era of watch and wait), (2) Preoperative or neoadjuvant therapy for down-staging of a tumor to facilitate R0 resection and to sterilize microscopic disease (e.g., locally advanced rectal cancer, FIGO stage IIIB endometrial cancer), and (3) Postoperative or adjuvant therapy to sterilize microscopic or gross residual disease after surgery (e.g., FIGO stage III/IVA endometrial cancer, node-positive cervix cancer after radical hysterectomy). When radiotherapy is sequenced with surgery, the surgical team must be aware of the acute and late toxicities of radiation treatment and the implications these may have on their operation, as well as the risk of peri-operative complications. This chapter describes the major potential toxicities of pelvic radiation therapy, acute and late, by organ site. Strong communication between the radiation oncology and surgical teams can help facilitate optimal timing of treatments and management of complications.