With recent changes in the landscape of health care, clinical practice guidelines (CPGs) have proliferated. Attitudes about guidelines differ considerably, forming 2 competing viewpoints with considerable tension between them. Some feel CPGs are unneeded or are efforts to create automated “cookie cutter” medical practice; at best, they are perceived as suggestions that may be altered by experience. Others feel they are mandates that must be followed to the letter. This article attempts to explain how and why we have arrived at this point and to explain the origins of the differing viewpoints. We begin by describing the 2 viewpoints and proceed to define the origin of medicine as a profession and to chronicle the evolution of health insurance, medical education, and scientific methods for evaluating evidence.