The POSITIVE Study brings together researchers across Canada and is one of 6 projects and 3 cores that constitute the Canadian Institute of Health Research (CIHR) funded interdisciplinary research program called the Canadian National Transplant Research Program (CNTRP). The CNTRP is a national program designed to increase organ and tissue donation in Canada and enhance the survival and quality of life of Canadians who receive transplants. As a national program, CNTRP provides robust power for pediatric studies that would not otherwise be possible. While primarily focused on issues unique to a pediatric and young adult population, this study will interact closely with all other CNTRP projects. These reciprocal interactions will accelerate new discovery that can be cross-applied in different populations outside of pre-specified age groups. Interactions will ensure rapid knowledge transfer, uptake and dissemination into practice. This is the largest national cohort study of pediatric transplant patients to date in Canada, and it will create a longitudinal dataset with clinical and biological specimens linkable to transplant registries and provincial administrative datasets.