The Rethinking Theorizing in Implementation Science (RTIS) Symposium 2026 welcomes everyone working in implementation — researchers, practitioners, policy partners, and community members — to come together and explore how theory can help us better understand and improve what we do. Our goal is clear: to spark curiosity and build shared excitement about the role of theory in implementation science, and to collectively consider how we can promote more creative, practical, and meaningful use of existing theory as well as develop new theory across our work.