Acute kidney injury (AKI) is one of the most frequently encountered and prognostically significant complications after cardiovascular surgery. However, there is no definitive treatment to intervene after development of AKI, therefore, preventive strategy has been the major issue. By this time, incidence of AKI after cardiovascular surgery has been reported 3-50% based on the studies with various definition of AKI and different patient cohorts. Development of unified definition for AKI in the early 2000s opened a new era in AKI study.