| Progress in renal transplantation requires improved understanding and assessment of rejection and injury. Study of the relationship between gene expression and clinical phenotypes in kidney transplant biopsy samples has led to the development of a system that enables diagnoses of specific disease states on the basis of messenger RNA levels in the biopsy sample. Using this system we have defined the molecular landscape of T cell-mediated rejection (TCMR), antibody-mediated rejection (ABMR), acute kidney injury (AKI), and tubular atrophy and interstitial fibrosis. TCMR and ABMR share IFNγ-mediated effects and TCMR has emerged as a cognate T cell-antigen presenting cell process in the interstitium, whereas ABMR is a natural-killer-cell-mediated process that occurs in the microcirculation. The specific features of these different processes have led to the creation of classifiers to test for TCMR and ABMR, and revealed that ABMR is the principal cause of kidney transplant deterioration. The molecular changes associated with renal injury are often more extensive than suggested by histology and indicate that the progression to graft failure is caused by continuing nephron injury, rather than fibrogenesis. In summary, advances in the molecular assessment of disease states in biopsy samples has improved understanding of specific processes involved in kidney graft outcomes.