Acute kidney injury (AKI) is a common condition in the intensive care unit (ICU) and approximately 5~10% of such patients require renal replacement therapy (RRT), with the mortality rates of 30~ 70%. Continuous renal replacement therapy (CRRT) is one of the common methods of renal support for critically ill patients with AKI, particularly patients who are hemodynamically unstable. In South Korea, more than 80% of cases of acute renal replacement therapy were reported as CRRT after 2014. To date, the optimal modality of CRRT for AKI is unknown and clinical practice is highly variable worldwide; target patient population, timing of treatment, CRRT technique (CVVH, CVVHD, or CVVHDF), treatment dose (estimated small solute clearance), choice of membrane, and mode of anticoagulation. This lecture will introduce differences in CRRT implementation around the world based on the previously published data by BEST kidney investigators, and the results of the recent European Society of Intensive Care Medicine (ESICM) survey. At the end of this lecture, recently proposed research topics regarding CRRT modalities will be also introduced.