Part 1 of this thesis focuses on immunosuppression after kidney transplantation. The optimal immunosuppressive regimen for kidney transplant recipients is a subject of active research. Corticosteroids are very effective in preventing rejection, but have severe side effects. In this thesis, we show that early steroid withdrawal is a safe short term immunosuppressive strategy for kidney transplant recipients with a low to intermediate immunological risk. A more intensive immunosuppressive regimen has also made it possible to perform kidney transplantations across the blood barrier. We compared ABO incompatible to ABO compatible transplantations and found that ABO-incompatible kidney transplant recipients had a slightly lower kidney function three months after transplantation, but the same rate of kidney function decline during five-year follow-up. This may be due a higher rate of early rejection, which was surprisingly mostly T-cell mediated, possibly as a result of ongoing complement activation. In Part 2 of this thesis, we analyzed the effects of chronic kidney disease and kidney transplantation on cognitive function and quality of life. We found that the quality of life in hemodialysis patients is comparable to hematological patients undergoing chemotherapy. Kidney transplant patients reported a large positive health change, but still had a lower quality of life than healthy controls, comparable to hematological patients in remission. Finally, we investigated the effects of kidney transplantation on cognitive function and found that kidney transplantation resulted in improved scores on tasks measuring attention and working memory, which was associated with an improvement in white matter integrity on MRI scans.