The Arc is the largest national community-based organization devoted to advocating for and serving individuals with intellectual and developmental disabilities (ID/DD) and their families. The organization has more than 700 chapters nationwide and serves people of all ages and with over 100 different diagnoses, including autism spectrum disorder, Down syndrome, and fragile X syndrome, among others. This entry first provides a brief history of the organization and information about the mission and core values of The Arc. It then describes the organization’s programs and services, including public policy, training, and other efforts to promote the well-being of individuals with ID/DD.