In the past, ABO incompatibility has been considered an absolute contraindication for living donor kidney transplantation. Over the past 25 years, advances in immunosuppressive therapy and progressively more refined desensitization protocols have allowed increasingly successful transplantations across the ABO barrier. Current results of kidney transplants from ABO-incompatible living donors are quite favorable and comparable in the long term with the outcome of ABO-compatible organs both in Japan and in the United States. The present article reviews the history, outcomes, and current issues in kidney transplantation with ABO-incompatible living donors in adult and pediatric recipients.