This paper describes the origins and evolution of the term radical behaviorism. John B. Watson's coining of behaviorism in 1913 is presented first, followed by a discussion of the uses of "radical" within psychology during these early years. When the term radical behaviorism first emerged in the early 1920s, its referent was Watson's behaviorism, most specifically his stance on consciousness. In the 1930s, B. F. Skinner described his own position with the term radical behaviorism in an unpublished manuscript, and then in 1945 first referred in print to his views as such. Today, radical behaviorism is generally applied to Skinner's views alone. The paper concludes with a brief discussion of a similarity in Watson's and Skinner's positions on consciousness, which seems a possible historical and philosophical connection between their respective radical behaviorisms.