Continuous Renal Replacement Therapy (CRRT) is a form of dialysis provided to critically ill patients with acute renal failure, now known as acute kidney injury (AKI). While we have extensive experience with this therapy in critically ill patients, there is no consensus on when to start CRRT or a clinical standard as to the best possible way to deliver the therapy. Previous studies have examined one aspect of CRRT in detail (for instance the dose of delivered therapy, or anticoagulation strategies) or have been small single center studies, or large multinational studies examining very basic practice patterns. This is a prospective observational cohort study. All patients who receive CRRT as part of their standard of local care will be eligible for the study.