Haemostasis refers to the cessation of bleeding, which is achieved by a complex arrangement of balanced interactions between blood cells, the vasculature, plasma proteins and low molecular weight substances. A system of checks and balances ensures that, although a thrombus (clot) is formed and protected at the site of vessel damage to stop bleeding, vessel occlusion (thrombosis) is prevented. Haemostasis represents an equilibrium between the opposing processes of bleeding on the one hand and hypercoagulability and thrombosis on the other. Unbalanced or altered haemostasis most often tends towards haemorrhage, but when excessive thrombosis occurs it may cause significant disease. As a general overview, bleeding following vascular injury must be stopped to prevent excessive blood loss. This chapter considers the following topics: Stages of haemostasis; Pathophysiology of altered haemostasis; Assessment of haemostasis in the surgical patient; and Blood component therapy. Also included are techniques for the buccal mucosal bleeding time (BMBT) test; Feline in-house cross-match procedure; Canine whole-blood collection procedure; and Blood collection via syringe.