Relationship Development Intervention (RDI) is a behavioral treatment designed to reduce the core symptoms of autism spectrum disorder (ASD). Specifically, RDI uses a parent-mediated approach with a focus on developing personal relationships by gradually and systematically strengthening the foundational skills of social connections. This includes the ability to form an emotional bond and share experiences. In addition, RDI addresses key core issues such as motivation, communication, emotional regulation, episodic memory, rapid attention shifting, self-awareness, appraisal, executive functioning, flexible thinking, and creative problem solving. This entry provides a brief history of the development of RDI, as well as the theoretical underpinnings of the model and its application.