In Chapter 1, I discuss scientism, or the belief that scientific knowledge is the most (or only) legitimate form of knowledge. My argument is that scientism mischaracterizes science as an epistemically privileged and unified method. Actual scientific practice, however, has demonstrated tremendous variability in theory and method across time, place, and disciplinary context, and can best be understood as a historically contingent human activity. Drawing on historical and philosophical critiques, I characterize scientism as a kind of science fundamentalism that insulates scientists from social and moral critique and so contributes to the institutionalization of exceptionalism and privilege. I discuss elements of scientism in professional psychology, using historical and contemporary examples to show that it is a common (perhaps even a majority) position.