There are multiple different ways to define AKI. A generally accepted definition is that put forth by the Kidney Disease Improving Global Outcomes group. They define AKI in 2 ways - by change in function (serum creatinine) and/or by urine output. This is well described by the Kidney Disease Improving Global Outcomes group. The KDIGO guidelines stage AKI by severity which is predictive of important kidney outcomes AKI can also be defined categorically by where the injury is happening relative to the kidney (pre-renal, renal, post-renal). Defining in this way can be helpful in terms of differential diagnosis/identifying cause(s) of AKI. A more practical, clinical approach to AKI is that of functional vs tissue level injury. Similar ways of thinking of this could be mild vs severe, quickly reversible vs prolonged or irreversible, early vs late, etc. The mainstay of AKI management is determination of whether or not urine is being made at a reasonable amount. If anuria/oligoanuria is observed, more than likely renal replacement therapy will be indicated. Diuretic stress test using loop diuretics can help to determine if oliguria/anuria present. If a response is observed with high dose loop diuretics, the injury is likely less severe and recovery without RRT may occur. AKI management involves determine cause(s), assessing severity, managing possible trouble to occur from low kidney function (hyperkalemia, pulmonary edema) as well as preventing further injury. Optimizing hemodynamics, avoiding nephrotoxins, and renally dosing medications is critical. These patients should be evaluated by nephrologists in the hospital and followed up in the ambulatory setting. AKI is an important clinical event portending significant kidney, cardiovascular and mortality outcomes. Ongoing efforts to prevent and diagnose AKI earlier are being made to reduce the burden it this common serious entity.