This chapter covers acute myeloid leukaemia (AML) and acute lymphoblastic leukaemia (ALL), and includes information on prognostic factors, current standard of care, basic biology, epidemiology, clinical presentation, diagnosis, pathophysiology, aetiology, and management. Although the majority of patients with acute myeloid leukaemia (AML) achieve complete remission with induction chemotherapy, relapse after achievement of clinical remission remains the most critical clinical challenge facing AML patients and clinicians today, with a pressing need to improve prognostication. Prognostic factors in acute lymphoblastic leukaemia is to stratify patients into good- and poor-risk groups and to adapt different treatment strategies accordingly. There are principally two phases to evaluating prognostic factors; the first is the patient characteristics at diagnosis and the second is the response to treatment.