Despite interest from both radiation oncology residents and program directors, many residency training programs lack a formalized introductory curriculum to orient incoming radiation oncology residents to the specialty. Using the 6-step model for medical education curriculum development, a structured introductory radiation oncology curriculum (IROC) was created for incoming post-graduate year 2 (PGY-2) radiation oncology residents to address foundational concepts including patient simulation, contouring, and plan evaluation. The curriculum was distributed to 55 training programs across the United States and Canada at the start of the 2018 to 2019 and 2019 to 2020 academic years. Feasibility of curriculum dissemination was assessed via a survey of participating program directors. Curriculum effectiveness was assessed using an anonymous survey of participating residents administered pre- and postcurriculum and consisting of both subjective and objective knowledge-based questions. A total of 236 residents participated in IROC at the start of the 2018 to 2019 and 2019 to 2020 academic years. Of those, 228 of 236 (97%) completed both the pre- and postcurriculum surveys. Of participating residents, the median residency program size was 10 (range, 2-28), and the median number of residents in each program per year was 3 (range, 1-7). At baseline, most PGY-2s (142 of 228, 62%) reported being "not at all" or "slightly" prepared to function in the radiation oncology clinic, and after IROC most (188 of 228, 82%) felt "moderately," "quite," or "extremely" prepared. Objective knowledge improved pre- to postcurriculum on a multiple-choice test from 70% to 81% (P < .0001) correct, with improvements observed across all question items. Program directors also reported that the curriculum was easier to use and more effective than prior orientation materials. The implementation of an international introductory curriculum for PGY-2 radiation oncology residents is both feasible and effective. Similar strategies should be employed to enhance and standardize radiation oncology educational initiatives across training programs.