Surgery and anesthesia profoundly alter the normal physiologic and metabolic states. Estimating the patient’s ability to respond to these stresses in the postoperative period is the task of the preoperative evaluation. Perioperative complications are often the result of failure, in the preoperative period, to identify underlying medical conditions, maximize the patient’s preoperative health, or accurately assess perioperative risk. Sophisticated laboratory studies and specialized testing are no substitute for a thoughtful and careful history and physical examination. Sophisticated technology has merit primarily in confirming clinical suspicion.