This guideline aims to summarise the current literature guiding the use of red cell transfusion in critically ill patients and provides recommendations to support clinicians in their day-to-day practice. Critically ill patients differ in their age, diagnosis, co-morbidities, and severity of illness. These factors influence their tolerance of anaemia and alter the risk to benefit ratio of transfusion. The optimal management for an individual may not fall clearly within our recommendations and each decision requires a synthesis of the available evidence and the clinical judgement of the treating physician.