This paper describes research and development efforts related to adaptive technologies, which can be combined with other technologies and processes to form an adaptive system. The goal of an adaptive system, in the context of this paper, is to create an instructionally sound and flexible environment that supports learning for students with a range of abilities, disabilities, interests, backgrounds, and other characteristics. After defining key terms and establishing a rationale for adaptation, we present a general framework to organize adaptive technologies. We then describe experts' thoughts on what to adapt and how to adapt and conclude with a summary of key challenges and potential futures of adaptive technologies.