Histocompatibility is the biological property describing the degree of compatibility between the tissues of a donor and a recipient, particularly concerning the potential for the recipient's immune system to recognize and reject the donor tissue. This concept, central to immunology and transplantation biology, investigates the genetic determinants of tissue compatibility, notably the polymorphic genes of the major histocompatibility complex (MHC; HLA in humans). The field examines the mechanisms of immune recognition, the factors influencing graft acceptance or rejection, and strategies to overcome incompatibility, holding significant importance for the success of transplantation procedures and the study of immune system function.