Although blood transfusion saves lives and reduces morbidities in many clinical diseases and conditions, it is associated with certain risks. A transfusion-related adverse event, also called transfusion reaction, is any unfavourable event occurring in a patient during or after blood transfusion. About 0.5% to 3% of all transfusions result in some adverse events, but the majority of them are minor reactions with no significant consequences. In general, transfusion-related adverse events are categorised as infectious and non-infectious. However, there are other classifications in the literature based on time of occurrence (i.e. acute versus delayed) or physiological mechanism (i.e. immune mediated versus non-immune mediated). A significant proportion of adverse events may occur as a result of errors in preparation, ordering or administration of blood and blood products. This book contains the latest research in this essential field which has been revolutionised in recent decades.