Postoperative bleeding is a major cause of early morbidity, reoperation, and transfusion in surgical patients. While surgical bleeding from inadequate hemostasis or vessel injury is common, coagulopathy due to hemodilution, hypothermia, acidosis, consumption, fibrinolysis, and drug effects frequently coexists and amplifies blood loss. The perioperative period uniquely predisposes to hemostatic derangements via crystalloid/colloid resuscitation, cardiopulmonary bypass (CPB), massive transfusion, and inflammatory responses that disrupt platelet function, coagulation factors, fibrinogen, and endothelial integrity. Early recognition requires structured assessment: bedside clinical cues, standard labs (e.g., complete blood count, prothrombin time (PT)/international normalzied ratio (INR), aPTT, and fibrinogen), and increasingly, viscoelastic testing (e.g., thromboelastography (TEG) and rotational thromboelastometry (ROTEM)) to characterize clot initiation, strength, and lysis. Management hinges on two simultaneous priorities: (1) prompt surgical or procedural hemostasis when indicated and (2) targeted, physiology-guided correction of hemostatic defects (e.g., temperature, calcium, and pH), factor replacement (e.g., fresh frozen plasma, prothrombin complex concentrates, etc.), platelet therapy, and fibrinogen repletion (e.g., cryoprecipitate or fibrinogen concentrate). Antifibrinolytics (e.g., tranexamic acid) are valuable in hyperfibrinolysis and high-risk settings (e.g., in trauma, obstetric hemorrhage). Reversal strategies for antithrombotic medications must be algorithmic and timely. Transfusion carries risks (e.g., transfusion-related Acute lung injury (TRALI), transfusion-associated circulatory overload (TACO), citrate toxicity, hypocalcemia, immunomodulation, etc.) and should be embedded within patient blood management programs emphasizing restrictive triggers and multimodal strategies. This chapter reviews mechanisms, risk stratification, diagnostic frameworks, targeted treatments, and postoperative monitoring, with special attention to CPB-associated coagulopathy, massive transfusion, liver disease, and renal dysfunction.