This chapter discusses haematological disorders and includes discussion on bleeding disorders (including acquired bleeding disorders and inherited bleeding disorders), anaemia in critical care (including discussion on pathogenesis, consequences of anaemia, approach to the investigation of anaemia, classification of anaemia, measures to minimize blood loss in the intensive care unit [ICU], and erythropoietin). It also covers sickle cell anaemia (transfusion in sickle cell anaemia, including hyperhaemolysis, acute chest syndrome, and pulmonary hypertension in sickle cell disease), haemolysis (haemolytic conditions particularly relevant to critical care), disseminated intravascular coagulation, neutropenic sepsis (including persistent fever or inadequate clinical response, fungal infections, empirical antifungal therapy, viral infections, granulocyte-colony stimulating factor, and granulocytes for neutropenia). Finally, the chapter discusses haematological malignancies in the ICU (neutropenia and neutropenic sepsis, tumour lysis syndrome, hyperviscosity syndromes, hyperleukocytosis, haemorrhagic complications, haematopoietic stem cell transplant, graft versus host disease, and corticosteroids) and coagulation monitoring.