Kidney dysfunction causes a myriad of adverse influences on posttransplant outcomes necessitating accurate assessment of kidney function for patient management. This evaluation assists in guiding treatment decisions, with the ultimate aim of allaying renal function decline. In clinical practice, renal function is typically estimated from serum creatinine levels, creatinine-based estimation equations or creatinine clearance; however, each of these methods has demonstrated limitations when used in the kidney transplant setting. Equally important is the emerging recognition of the incidence and impact of kidney dysfunction in recipients of nonrenal solid organ transplantation. The performance of commonly used estimation equations and methods for measuring kidney function in renal and liver transplant patients are overviewed here along with their potential roles in clinical transplantation.