The comprehensive identification and delineation of organs at risk (OARs) are vital to the quality of radiation therapy treatment planning and the safety of treatment delivery. This guidance aims to improve the consistency of ontouring OARs in external beam radiation therapy treatment planning by providing a single standardized resource for information regarding specific OARs to be contoured for each disease site. The guidance is organized in table format as a quality assurance NotedEarn CME credit by taking a brief online assessment at https://www.astro.org/JournalCME. Disclaimer and Adherence: ASTRO clinical practice statements present scientific, health, and safety information and may reflect scientific or medical opinion. They are available to ASTRO members and the public for educational and informational purposes only. Commercial use of any content in this paper without the prior written consent of ASTRO is strictly prohibited.Adherence to this guidance will not ensure successful treatment in every situation and should not be deemed inclusive of all proper methods of care or exclusive of other methods reasonably directed to obtaining the same results. The physician must make the ultimate judgment regarding any specific therapy in light of all circumstances presented by the patient. ASTRO assumes no liability for the information, conclusions, and findings contained in its papers. This guidance cannot be assumed to apply to the use of these interventions performed in the context of clinical trials.This guidance is based on information available at the time the task force conducted its research and discussions on this topic. There may be new developments that are not reflected in this guidance and that may, over time, be a basis for ASTRO to revisit and update the paper.Sources of support: This paper was funded by the American Society for Radiation Oncology. Conflicts of interest: Before initiation of this paper, all members of the Task Force and Review Panel completed disclosure statements. These statements are maintained at ASTRO Headquarters in Arlington, Virginia. ASTRO's Clinical Affairs and Quality Council reviewed these disclosures and determined they do not present a conflict with respect to the Task Force members' work on this consensus paper. Jean Wright: ASTRO (honoraria),