Acute kidney injury is common entity in medical practice. The present definition is based on a serum creatinine rise of more 0.3 mg/dl in 48 hours or less, a 50% increase from the baseline over a period of 07 days or a urine output of less than 0.5 ml/kg/hour for more than 06 hours. The main causes of acute kidney injury may be classified into pre renal, intrinsic or post renal causes. Rapid diagnosis and prompt treatment is essential to prevent mortality or morbidity. This presentation discusses in detail the causes of all three mechanisms, pre-renal, post renal and intrinsic.