Blood transfusion is widely considered a pillar of modern medicine and is one of the most common medical interventions. A transfusion intimately links two persons and their health through the altruism of blood donors. In turn, this has necessitated the development of rigorous safety measures for both donors and recipients. Hemovigilance is the systematic surveillance of adverse events in the entire blood supply chain, stretching from blood donation to transfusion and follow-up care. Although transfusion safety has dramatically improved in recent decades, especially in regard to transfusion-transmitted infections, there are still evidence gaps for many aspects of blood donation and transfusion safety. This thesis explores several aspects of current controversies in both blood donation and transfusion safety and proposes a ‘big-data’approach to hemovigilance with the use of data from electronic healthcare records and health registers, and provides a data-driven method for calculating longitudinal transfusion costs.