Renal biopsy is an invasive diagnostic technique essential for the treatment of nephrology patients. Through the histological analysis of the renal tissue an etiological diagnosis can be performed, a prognosis can be issued and the therapy of the majority of parenchymal nephropathies can be oriented, both for native kidneys as well as kidney transplants. This latter group also in­cludes protocol biopsies, above all in clinical trials, which merit a separate discussion.