Understanding of coagulation and coagulopathy is essential to the practice of anesthesia. This begins with preoperative assessment and planning. A detailed history is the first step. Laboratory testing can reveal abnormalities that may have otherwise gone undetected, as many disorders are asymptomatic until unmasked by the stress of surgery. Some of these disorders may be inherited or acquired, and their presentation and treatment must be considered. Intimate familiarity of this topic allows the anesthesiologist to adequately prepare for coagulopathy and thrombotic events in the perioperative environment.