Acute kidney injury (AKI) is a critical condition where the kidneys rapidly decline in function over hours or days, causing waste and water to accumulate. It affects millions worldwide annually. AKI can be pre-renal from decreased blood flow, intra-renal from direct kidney damage, or post-renal from urinary tract obstruction. It is diagnosed through medical history, lab tests, and imaging and treated by addressing underlying causes, fluid/electrolyte management, and sometimes dialysis or transplantation. Risk factors include age, vascular diseases, diabetes, and previous kidney injuries.