Increases in the patients on the organ transplant wait list have far out paced the number of available organs. This has lead to longer time awaiting transplantation and thus increased morbidity and mortality associated with it. Making more organs available for transplantation remains critical, and hence, extended criteria donors and ABO-incompatible organs are being utilized. Recent reports on the use of conventional immunosuppressive regimens for ABO-incompatible grafts suggest outcomes can be obtained similar to those of ABO-compatible transplants. The delay in the development of natural antibodies to ABO antigens in infants provides an 'immunological window' that allows for successful ABO-incompatible transplants in this age group. This also allows for a unique mechanism long-term tolerance to the graft in infants. ABO incompatibility may no longer be a contraindication in case of kidney transplantation and paediatric heart transplantation. Increased utilization of ABO-incompatible grafts can alleviate the shortage for organs and decrease waitlist times and associated morbidity. In this review, we will discuss the current status of ABO-incompatible transplantation in adult and paediatric solid organ transplantation with attention on recent developments on understanding the mechanisms of graft acceptance in these ABO-incompatible organs.