BACKGROUND AND OBJECTIVES: Cognitive benefits of longitudinal curricula and interleaving have been demonstrated in several disciplines. However, most residency curricula are structured in a block format. There is no consensus definition as to what constitutes a longitudinal program, making comparative research on curricular efficacy a challenge. The objective of our study was to arrive at a consensus definition of Longitudinal Interleaved Residency Training (LIRT) in family medicine. METHODS: A national workgroup was convened and utilized a Delphi method between October 2021 and March 2022 to arrive at a consensus definition. RESULTS: Twenty-four invitations were sent, and 18 participants initially accepted. The final workgroup (n=13) was representative of the nationwide diversity of family medicine residency programs in terms of geographic location (P=.977) and population density (P=.123). The following definition was approved: LIRT is a curricular design and program structure that offers graduated, concurrent clinical experiences in the core competencies of the specialty. LIRT models the comprehensive scope of practice and continuity that defines the specialty; applies training methods that enhance long-term retention of knowledge, skills, and attitudes across all dimensions and locations of care delivery; and accomplishes program objectives through employment of longitudinal curricular scheduling and interleaving with spaced repetition. Additional technical criteria and definitions of terms are elucidated in the body of this article. CONCLUSIONS: A representative national workgroup crafted a consensus definition of Longitudinal Interleaved Residency Training (LIRT) in family medicine, a program structure with a basis in emerging evidence-based cognitive science.