John B. Watson was a central figure in the early twentieth-century development of psychology and is often credited as the founder of behaviorism—he did coin the terms behaviorism and behaviorist. This entry examines his career from his early work in comparative psychology at the University of Chicago and at Johns Hopkins University to his later publications in the popular media after leaving academia. Watson’s conceptual framework rejected consciousness and introspection, advocating instead for the study of observable behavior through habit formation and later stimulus-response processes. Although his popular writings were controversial and often lacked empirical grounding, they helped shape public perceptions of behaviorism. Watson’s behaviorism was never dominant in academic psychology, but it laid the groundwork for later developments in behavioral science. His lasting influence lies in promoting behavior as a legitimate scientific subject and psychology as a natural science, even if later behaviorists distanced themselves from many of his main claims. Watson’s work remains a key reference in the historical understanding of psychological science.