OBJECTIVES: To develop an initial list of characteristics of life course interventions to inform the emerging discipline of life course intervention research. METHODS: The Life Course Intervention Research Network, a collaborative national network of >75 researchers, service providers, community representatives, and thought leaders, considered the principles, characteristics, and utility of life course interventions. After an in-person launch meeting in 2019, the steering committee collaboratively and iteratively developed a list of life course intervention characteristics, incorporating a modified Delphi review process. RESULTS: The Life Course Intervention Research Network identified 12 characteristics of life course interventions. These interventions (1) are aimed at optimizing health trajectories; (2) are developmentally focused, (3) longitudinally focused, and (4) strategically timed; and are (5) designed to address multiple levels of the ecosystem where children are born, live, learn, and grow and (6) vertically, horizontally, and longitudinally integrated to produce a seamless, forward-leaning, health optimizing system. Interventions are designed to (7) support emerging health development capabilities; are (8) collaboratively codesigned by transdisciplinary research teams, including stakeholders; and incorporate (9) family-centered, (10) strengths-based, and (11) antiracist approaches with (12) a focus on health equity. CONCLUSIONS: The intention for this list of characteristics of life course interventions is to provide a starting point for wider discussion and to guide research development. Incorporation of these characteristics into intervention designs may improve emerging health trajectories and move critical developmental processes and pathways back on track, even optimizing them to prevent or reduce adverse outcomes.