Haemovigilance (HV) comprises surveillance procedures covering the whole transfusion chain from collection of blood (components) to follow-up of its recipients. It assesses information on undesirable transfusion effects to prevent their occurrence. This includes local venepuncture accidents, iron depletion, graft vs. host disease and mild to severe transfusion reactions. The HV definitions aim to standardize and report all these events in order to improve blood safety.