 Background: In renal allograft recipients, 10-year graft survival has not much improved over the past decades. There is thus a need for robust, non-invasive methods to predict and diagnose acute and chronic graft lesions, to improve patient treatment, quality of life and long-term graft survival. Also, there is an unmet need for better understanding of the immune and non-immune mechanisms of interstitial fibrosis tubular atrophy and graft loss. Several teams have searched for biomarkers of renal graft lesions, but there has been no cross-fecundation of the different omics approaches, nor any consolidation of the different clusters of biomarkers discovered using different technologies. An analysis of these different omics levels based on the principles of systems biology is therefore necessary to gain insight into the disease mechanisms and will help to develop predictors at the individual level. Purpose: The European project BIOMARGIN aims to discover, select and validate blood andor urine biomarkers of renal allograft lesions in adult and paediatric kidney transplant recipients by integrating several omics approaches mRNA, miRNA, peptides, proteins, lipids and metabolites in blood, graft tissue and urine. The European cohort study BECS aims to evaluate the diagnostic and prognostic performance of the selected biomarkers over the first 3 and 5 years post-transplantation. Study design: This is a multicenter, international, ambispective, open and non-interventional cohort study, with collection of biological samples. Number of subjects: 450 adult and 50 paediatric renal transplant recipients. Outcomes: The primary endpoint is the graft outcome, assessed at three years as any lesion appeared on graft biopsies after patient enrolment, decline in graft function 30, graft loss or patient death. Secondary endpoints include: histological findings in indication biopsies as well as in systematic biopsies as per centre procedures at 5 years; cumulated acute rejection episodes; 3-year and 5-year graft survival; and change of renal function assessed by the glomerular filtration rate GFR estimated using the MDRD formula. Statistical analysis: The sensitivity, specificity, positive and negative predictive values of the different biomarkers or sets of biomarkers will be evaluated for each of the primary and secondary endpoints. In order to compare the performance of the biomarkers with those of the other known risk factors for the deterioration of renal graft function, longitudinal statistical modelling will be used. 