Correct determination of glomerular filtration rate (GFR) as an indicator of kidney function bears great importance because clinical decision-making depends on it at many occasions. During the last years, a huge body of literature has been published on estimation and measurement of GFR. The increasing pace with which novel estimation formulae, current and newer biomarkers, assay standardization procedures as well as invasive measurement methods of GFR were published, has been overwhelming for many clinicians.