Acute renal failure on the intensive care unit is generally multifactorial in origin. Renal failure affects a number of patients in intensive care and carries significant morbidity and mortality. The prognosis is worse when renal failure occurs as part of multi-organ failure. There are two main categories of renal failure: acute and chronic renal failure. Different systems of staging acute kidney injury (AKI) are available. They include the Acute Kidney Injury Network (AKIN), RIFLE and Kidney Disease Improving Global Outcomes (KDIGO) criteria. Renal replacement therapy seeks to artificially mimic the excretory function of the kidney. The common thread among all methods is use of a semipermeable membrane for filtration. Various modes of delivering renal replacement therapy include peritoneal dialysis, haemodialysis, and haemofiltration. Drug pharmacokinetics in patients on renal replacement therapy can be very complex and differ from patients not on renal replacement. Dose and frequency of administration also vary between haemodialysis and haemofiltration.