This study focuses on adults and children who have been diagnosed with focal segmental glomerulosclerosis (FSGS) or minimal change disease (MCD) and who have had or are scheduled to have a kidney transplant. The purpose of the study is to create a bank of information and biospecimens so that researchers can more effectively study FSGS and MCD. FSGS is a condition in which scarring of the filters in the kidneys that remove waste from the blood occurs. MCD causes large amounts of protein to be lost in urine. After a kidney transplant, sometimes FSGS and MCD return in the new kidney. Researchers aim to understand why this happens in some people but not in others. Participants will complete enrollment and follow-up visits, in addition to procedures such as collection of blood, urine, saliva, and kidney tissue (excess tissue from biopsy or past kidney biopsy tissue images). Medical records will also be reviewed.