Transplantation immunology is a unique field that studies its immune response which occurs artificially after organ transplantation; Although it is a basic medical science, but a field in which the clinical department must be involved. In the case of lung transplantation, although the organ is connected to the outside environment, it requires a large dose of immunosuppressive drugs due to its own strong defense mechanism. However, the prognosis for lung transplantation is much poorer than for other solid organ transplants due to chronic lung allograft dysfunction (CLAD), which still occurs in more than 50% of transplant recipients. Prevention of CLAD without immunosuppressive drugs is urgently needed, and it is important to study its immunological pathogenesis. In this chapter, as the basis of lung transplantation immunology, it was described the unique defense mechanisms, the basic of immunology, risk factors for CLAD and their immunological mechanisms, and for the study of CLAD, biomarkers are mentioned from the clinical side and animal models from the experimental transplantation immunology.