In the early twentieth century psychology became the study of "behavior." This article reviews developments within animal psychology, functional psychology, and American society and culture that help explain how a term rarely used in the first years of the century became not only an accepted scientific concept but even, for many, an all-encompassing label for the entire subject matter of the discipline. The subsequent conceptual and linguistic activity of John B. Watson, Edward C. Tolman, Clark L. Hull, and B.F. Skinner, (...) as they attempted to explain "behavior" throughout the course of the twentieth century, is then discussed. Finally, the article suggests the need for greater conceptual and linguistic diversity in psychology. In this last regard, reference is made to cognition and consciousness, to William James and John Dewey, and to the fact that prediction and control might not be the most relevant aims of contemporary psychology. (shrink)