This chapter presents all aspects of haematology, including the history of haematology, iron-deficiency anaemia, anaemia of chronic disease, sideroblastic anaemia, peripheral blood film, differential white cell count, macrocytic anaemia, B12 deficiency and pernicious anaemia, haemolytic anaemia, sickle-cell anaemia, thalassaemia, bleeding disorders, coagulations pathways, blood transfusion and blood products, anticoagulants, leukaemia and the on-call junior doctor, acute lymphoblastic leukaemia, acute myeloid leukaemia, chronic myeloid leukaemia, chronic lymphocytic leukaemia, Hodgkin’s lymphoma, Non-Hodgkin’s lymphoma, pancytopenia and bone marrow failure, myeloproliferative disorders, myeloma, paraproteinaemia, amyloidosis, erythrocyte sedimentation rate (ESR), plasma viscosity (PV), hyperviscosity syndrome, spleen and splenectomy, thrombophilia, and immunosuppressive drugs.