Acute renal failure (ARF) is a common complication in critically ill patients, with ARF requiring renal replacement therapy (RRT) developing in approximately 5 to 10% of intensive care unit (ICU) patients. Epidemiological studies have demonstrated that ARF is an independent risk factor for mortality. Interventions to prevent the development of ARF are currently limited to a small number of settings, primarily radiocontrast nephropathy and rhabdomyolysis. There are no effective pharmacological agents for the treatment of established ARF. Renal replacement therapy remains the primary treatment for patients with severe ARF; however, the data guiding selection of modality of RRT and the optimal timing of initiation and dose of therapy are inconclusive. This review focuses on the epidemiology and diagnostic approach to ARF in the ICU and summarizes our current understanding of therapeutic approaches including RRT.