Objective: The primary objective of this trial is to study in a prospective randomized comparison whether a restrictive RBC transfusions strategy is non-inferior compared to a liberal strategy in patients on ECMO with respect to 90-day mortality. Study design: Prospective multi-center randomized controlled non-inferiority trial. Study population: Patients, 18 years or older, receiving ECMO. Intervention: Restrictive RBC transfusion threshold: in case the Hb transfusion trigger of 7.0 g/dL (4.3 mmol/L) is reached, 1 RBC unit at a time will be transfused. The aimed Hb target range of the restrictive/intervention group will be 7.1 - 9.0 g/dL (4.3 - 5.6 mmol/L). Liberal RBC transfusion threshold: in case the Hb transfusion trigger of 9.0 g/dL (5.6 mmol/L) is reached, 1 RBC unit at a time will be transfused. Target range of the liberal group is defined as Hb 9.1 - 11.0 g/dL Main study parameters/endpoints: The primary outcome parameter is 90-day all-cause mortality. Secondary outcomes include: 1) proportion of patients on ECMO exposed to allogeneic RBC transfusion; 2) RBC volume infused per patient during ECMO; 3) reasons for RBC transfusion other than Hb triggers; 4) transfusion reactions; 5) time on ECMO; 6) length of hospital- and ICU-stay; 7) in-ICU morbidity; 8) quality of life (QoL), iMTA Medical Consumption Questionnaire (iMCQ) and Productivity Cost Questionnaire (iPCQ) at 3, 6, 9, and 12 months; 9) costs related to a) transfusion, b) hospital admission and c) transfusion-related sequelae.