With an increase in the aging population worldwide, Korea is expected to become a super-aged society by 2026. The aging process has an impact on the kidneys. While aging does not directly cause kidney injury, structural and functional changes associated with normal aging may impair the reparative ability of the kidney, predisposing the elderly to a variety of renal illnesses. In addition, healthy aging and damage caused by disease often overlap in the kidneys, and their interactions are complicated.  In healthy aging, renal macrostructural changes include a decrease in cortical volume, an increase in surface roughness, and simple renal cysts. Microstructurally, the aging kidney exhibits nephrosclerosis including arteriosclerosis/arteriolosclerosis, global glomerulosclerosis, and interstitial fibrosis/tubular atrophy (IF/TA), which leads to the loss of nephron. This is distinguishable from chronic kidney disease (CKD), which may have segmental glomerulosclerosis, increased IF/TA density independent of %IF/TA, hypertrophy of remaining functional glomeruli, and albuminuria. In a longitudinal study of normal men, the decline in glomerular filtration rate (GFR), approximated by urinary creatinine clearance, was about 0.75 ml/min per year. CKD is currently defined by an eGFR<60 ml/min per 1.73 m2 or albuminuria (urine albumin-to-creatinine ratio≥30 mg/g) continuing for three months or more, which leads to a remarkable increase in the prevalence of CKD in elderly adults. The results from the large meta-analyses and numerous other studies, however, reveal that the GFR threshold at which the risk of mortality increases is not consistent across all ages. Mortality increases in elderly people with GFR<45 ml/min per 1.73 m2. Additionally, the absence of albuminuria in normal age-related eGFR reduction indicates that this functional drop may be not causally related to podocytopenia. Thus, several studies have recently suggested an age-adapted definition of CKD.  A better understanding of the aging kidney will contribute to the long-term maintenance of renal health and function throughout life as well as the management of the elderly with kidney disease.