Thromboelastography (TEG) is drawing more attention for clinical and in vitro studies of blood coagulation. It can be applied to evaluate the effects of both blood-soluble and insoluble biomaterials on whole blood coagulation from the beginning of coagulation through clot formation to the ending with fibrinolysis. TEG may also identify the relative contributions of various clotting factors, such as fibrinogen and platelets, to the overall coagulation process based on profiles of its variables using whole and partial blood components. A comprehensive review has been conducted on its applications for the assessment of a wide range of blood-contacting biomaterials ranging from polymers to ceramics and biomedical devices involved in many applications. The methodology is different in terms of instrumentation, the methods to activate blood coagulation, the type of blood (citrated versus fresh blood), and study settings (in vitro, in vivo, and clinical trials). The author's own work and future directions are discussed as well. TEG should be considered as one of the most useful tools for evaluating in vitro and in vivo blood-biomaterial interactions for different applications.