Diagnostic error is a challenging problem; addressing it effectively will require innovation across multiple domains of health care, including medical education. Diagnostic errors often relate to problems with clinical reasoning, which involves the cognitive and relational steps up to and including establishing a diagnostic and therapeutic plan with a patient. However, despite a call from the National Academies of Sciences for medical educators to improve the teaching and assessment of clinical reasoning, the creation of explicit, theory-informed clinical reasoning curricula, faculty development resources, and assessment tools has proceeded slowly in both undergraduate and graduate medical education. To accelerate the development of this critical element of health professions education and to promote needed research and innovation in clinical reasoning education, the Accreditation Council for Graduate Medical Education (ACGME) should revise its core competencies to include clinical reasoning. The core competencies have proven to be an effective means of expanding educational innovation across the United States and ensuring buy-in across a diverse array of institutions and disciplines. Reformulating the ACGME core competencies to include clinical reasoning would spark much-needed educational innovation and scholarship in graduate medical education, as well as collaboration across institutions in this vital aspect of physicianship, and ultimately, could contribute to a reduction of patient suffering by better preparing trainees to build individual, team-based, and system-based tools to monitor for and avoid diagnostic error.