Many professional societies publish clinical practice guidelines that pertain to the management of patients with specific diagnoses. This article explores clinical practice guidelines affecting emergency physicians, such as those published by the American College of Emergency Physicians and other medical specialty organizations, such as the American Heart Association. Examples of such guidelines include algorithms, such as those published in Advanced Cardiac Life Support, clinical decision rules, such as the Ottawa ankle rules, and pathways that describe the treatment of critical diseases such as acute myocardial infarction. This article discusses the relevance of these guidelines, algorithms, and protocols to the practicing emergency medicine specialist.