Acute kidney injury (AKI) is a common complication of acute illness and can affect between 30% and 60% of critically ill patients. It is associated with significant morbidity and mortality as well as a high cost to healthcare systems. There are a broad range of causes of AKI which should be considered in a systematic fashion, to avoid missing multiple potential causative factors. These include pre-renal causes from hypovolaemia, intrinsic renal causes such as glomerular diseases and post-renal obstructive causes. In the intensive care unit, two-thirds of AKI cases result from renal hypo-perfusion, sepsis and nephrotoxic agents; up to 5% will require renal replacement therapy. Modalities of renal replacement therapy include intermittent haemodialysis, peritoneal dialysis and continuous haemofiltration. Continuous haemofiltration is usually preferred in the intensive care setting, as it has greater haemodynamic stability and greater capacity to extract fluid from patients with fluid overload. Anticoagulation options can be achieved with systemic anticoagulation such as heparin or regional anticoagulation with citrate.