It is hoped that this guideline will serve as a resource and will stimulate investigators to conduct more research and to expand on the evidence base on the topic of anti- coagulation therapy for CPB. (Ann Thorac Surg 2018;105:650 62) 2018 by The Society of Thoracic Surgeons, International Anesthesia Research Society, and the American Society of ExtraCorporeal Technology The development of cardiopulmonary bypass (CPB) in the 1960s so successfully enabled open heart surgery that rigorous evidence-based clinical trials did not play a part in the initial phases of development [1]. After World War II, clinicians were faced with more and more treatment choices, to the point that uncertainty existed about the best options. Indeed, Archie Cochrane recognized the need for a more rigorousapproachtogivecliniciansanswerstokeyquestions about patient treatments. Cochrane s efforts eventually led to the formation of the Cochrane Collaboration as a re- pository of evidence-based summaries to answer important indeed requires, evidence to support surgeons in- terventions, preferably in the form of randomized controlled trials (RCTs). During the last 60-plus years since the intro- duction of clinical CPB as the foundation for performance of cardiac operations, surgeon investigators developed a safe, ef cient, and reproducible method of performing highly complex cardiac procedures using CPB. Many advances in CPB are the result of evidence-based RCTs. Others derive from prospective cohort studies and still others, from anec- dotal practice or consensus. Recognizing this large scope of practice and the varied nature of the evidence base to support the use of CPB, the Evidence Based Workforce of The Society of Thoracic Surgeons (STS) undertook a project to develop a series of practice guidelines that re ect the evidence base for the use of CPB in the current era. 