Haemostasis is a process in which a blood clot is formed in the wall of a damaged blood vessel. Haemostasis thus prevents blood loss while maintaining blood fluidity within the vascular system. The process includes a balanced cooperation of the elements of the vessel wall, blood platelets, and coagulation factors from blood plasma and damaged tissue cells. Haemostasis can be divided into primary and secondary haemostasis. Primary haemostasis includes initial vessel vasoconstriction immediately after the injury and the formation of a primary or white blood cloth from thrombocytes, encompassing the adhesion, activation, aggregation and secretion of thrombocytes. In the course of secondary haemostasis, which includes both coagulation and fibrinolysis, a definitive or red blood clot is irreversibly formed. Coagulation is a cascade of enzymatic chemical reactions among clotting factors from plasma that ends with the formation of a fibrillar network of fibrin, which strengthens the final clot. The central role in the coagulation cascade is played by thrombin that can either be formed by the intrinsic or the extrinsic pathway. Numerous positive feedback loops augment the efficacy of haemostasis. Simultaneously starts the process of fibrinolysis enabling final tissue and wound repair. Besides coagulation factors, anticoagulants must be present in plasma for an efficient haemostasis to occur. Haemostasis can be evaluated by specific laboratory tests which are prerequisite for further evaluation and treatment of patients. Different disturbances of haemostasis can be efficiently treated medically.