Acute kidney injury refers to sudden and often reversible loss of renal function, which develops over days or weeks. Azotemia refers to elevated levels of nitrogen-containing substances in the blood that accompany AKI, which include BUN and creatinine. Uremia refers specifically to the constellation of symptoms that occur with severe renal dysfunction. The etiologies of AKI are classified as prerenal, intrinsic renal, or post-renal, and there is a varied clinical presentation depending on the severity of kidney dysfunction. Acute kidney injury is diagnosed initially by a change in serum creatinine levels, and then the etiology is determined by clinical history, lab testing, imaging, and possibly kidney biopsy. The management of AKI depends on the etiology; however, attention to the individual's volume status and serum electrolytes is always important. If management is unsuccessful and AKI progresses to CKD, then renal replacement therapy with dialysis or kidney transplantation is necessary.