Guidelines have not always enjoyed such a preeminent role in health care. In the 1970s, for example, negligible high-quality research was available in the field of thrombotic disorders to inform decision-making for the limited diagnostic (lung scans and contrast venography for venous thrombosis) and therapeutic (unfractionated heparin, streptokinase, warfarin, and aspirin) resources available. With the explosion of scientific research in the 1980s, professional societies looked to CPGs as a way to help harried clinicians navigate complex and often conflicting primary studies to make informed medical decisions and counter administrative pressures to alter their practices in ways that might not be in their patients’ best interests. As recently as 1994, however, a survey of American College of Physicians members found that 43% of respondents believed CPGs would drive up health-care costs, 68% predicted guidelines would be used punitively to discipline physicians, and 34% believed guidelines would degrade the pleasure found in practicing medicine. Some professional societies at that time questioned the value of CPGs, especially in light of calls to increase the rigor—and consequently the cost—of methodologies for their development and implementation. With remarkable foresight, the American College of Chest Physicians (CHEST) in 2000 convened a workshop that examined the value of CPGs, decided they were worth the effort and expense, and set methodologic standards for their development and implementation. Since then, physicians have accepted CPGs as the terminus of the “knowledge funnel” through which research flows into systematic reviews and on to the development of guidelines, which are the “action” arm of science for improving clinical practice.