While the quality and quantity of research on service-learning has increased considerably over the past 20 years, researchers as well as governmental and funding agencies have called for more rigor in service-learning research. One key variable in improving rigor is using relevant existing theories to improve the research. The purpose of this article is to present a draft conceptual framework of relevant theories that can inform the study of service-learning effects on students. This proposed conceptual framework draws from theories, theory-based models and frameworks, and theory-based research. Practitioners and researchers are encouraged to review, test, and critique this proposed conceptual framework so as to advance the discussion regarding the use of relevant existing theories on service-learning research as well as practice.