Haemostasis stops bleeding whenever the vascular tree is broken. The first components that react to vascular injury are the platelets, which adhere to subendothelial structures, become activated and release various mediators that amplify platelet recruitment (platelet aggregation), eventually resulting in the formation of the platelet plug (primary haemostasis). The second important component of haemostasis is the coagulation process (secondary haemostasis), which is triggered by the exposure of blood to the extravascular tissue and, through a sequence of enzymatic reactions, leads to the generation of thrombin. The latter transforms fibrinogen into fibrin, a tridimensional structure consisting of intertwining fibres that stabilizes the platelet plug, thus achieving definitive haemostasis. Primary and secondary haemostasis are finely tuned by multiple mechanisms, whose function is strictly dependent on intact endothelium, which restrict the haemostatic plug formation to the injury site. Once the bleeding has stopped, repair of the injured vessel begins and, as the vascular integrity is restored, the fibrinolytic process solubilizes the haemostatic plug through the degradation of fibrin and protein bridges connecting platelets, eventually resulting in the “restitutio ad integrum” of the vessel wall. Congenital and acquired defects of primary or secondary haemostasis cause bleeding disorders of variable severity depending on the degree of the defect and the nature of the factor(s) involved.