Purpose Radiation Oncology Milestones 1.0 was developed in 2011 using the Accreditation Council of Graduate Medical Education's (ACGME) 6 core competencies to standardize the competency-based assessment of radiation oncology medical residents conducted by Clinical Competency Committees biannually. Critiques of Milestones 1.0 included the lack of clear progression between levels of the subcompetencies, and the complex language made it difficult to interpret by residents and faculty. The development of Milestones 2.0 aimed to simplify the language, clarify the expected progression of residents' competence, and provide supplemental resources for implementation. Methods The ACGME assembled a 9-member working group (academic radiation oncologists, residents, community members) to compose Milestones 2.0 for Radiation Oncology using a modified Delphi method consisting of multiple asynchronous small-group meetings interspersed with four web-based whole-group meetings until consensus was reached for each competency. Results Milestones 2.0 replaced disease-specific Patient Care subcompetencies (e.g., Lymphoma, Genitourinary) with those that emphasize the care delivery pathway (e.g., Consult, Simulation, Contouring and Target Delineation, Treatment Planning and Plan Evaluation, Treatment Delivery, Follow-up), restructured the Medical Knowledge competency, revised all subcompetency descriptions to chart a clear progression between levels, removed research from level 5 criteria, and provided a supplemental guide to aid implementation. Patient Care subcompetencies in Milestones 1.0 limited direct assessment of residents to specific rotations while revised subcompetencies in Milestones 2.0 can be assessed on every rotation. Level 5 in each subcompetency now reflects skills exhibited by the top 10% of residents and includes items such as "leads the multidisciplinary care team" under Consult. Previously, Medical Knowledge was an assessment of Medical Physics and Radiation/Cancer Biology. This has been modified to include Applied Sciences and Evidence-Based Foundations of Radiation Oncology with specific constructs to guide assessment. The supplemental guide gives real-life examples for each level within the subcompetencies to promote consistency in the implementation of Milestones 2.0 across residencies. The guide is designed as a living document to be tailored by programs to align with individual practices and allow for a shared mental model for faculty expectations. Discussion Milestones 2.0 builds on the foundation laid by Milestones 1.0 by aligning subcompetencies with clinical practice and represents a comprehensive approach to assessing core competencies necessary to succeed as a competent clinical radiation oncologist. The new framework will be put into practice in July 2022. Real-time feedback and additions to the supplemental guide will continue to refine and improve assessment of radiation oncology residents' clinical competence. Radiation Oncology Milestones 1.0 was developed in 2011 using the Accreditation Council of Graduate Medical Education's (ACGME) 6 core competencies to standardize the competency-based assessment of radiation oncology medical residents conducted by Clinical Competency Committees biannually. Critiques of Milestones 1.0 included the lack of clear progression between levels of the subcompetencies, and the complex language made it difficult to interpret by residents and faculty. The development of Milestones 2.0 aimed to simplify the language, clarify the expected progression of residents' competence, and provide supplemental resources for implementation. The ACGME assembled a 9-member working group (academic radiation oncologists, residents, community members) to compose Milestones 2.0 for Radiation Oncology using a modified Delphi method consisting of multiple asynchronous small-group meetings interspersed with four web-based whole-group meetings until consensus was reached for each competency. Milestones 2.0 replaced disease-specific Patient Care subcompetencies (e.g., Lymphoma, Genitourinary) with those that emphasize the care delivery pathway (e.g., Consult, Simulation, Contouring and Target Delineation, Treatment Planning and Plan Evaluation, Treatment Delivery, Follow-up), restructured the Medical Knowledge competency, revised all subcompetency descriptions to chart a clear progression between levels, removed research from level 5 criteria, and provided a supplemental guide to aid implementation. Patient Care subcompetencies in Milestones 1.0 limited direct assessment of residents to specific rotations while revised subcompetencies in Milestones 2.0 can be assessed on every rotation. Level 5 in each subcompetency now reflects skills exhibited by the top 10% of residents and includes items such as "leads the multidisciplinary care team" under Consult. Previously, Medical Knowledge was an assessment of Medical Physics and Radiation/Cancer Biology. This has been modified to include Applied Sciences and Evidence-Based Foundations of Radiation Oncology with specific constructs to guide assessment. The supplemental guide gives real-life examples for each level within the subcompetencies to promote consistency in the implementation of Milestones 2.0 across residencies. The guide is designed as a living document to be tailored by programs to align with individual practices and allow for a shared mental model for faculty expectations. Milestones 2.0 builds on the foundation laid by Milestones 1.0 by aligning subcompetencies with clinical practice and represents a comprehensive approach to assessing core competencies necessary to succeed as a competent clinical radiation oncologist. The new framework will be put into practice in July 2022. Real-time feedback and additions to the supplemental guide will continue to refine and improve assessment of radiation oncology residents' clinical competence.