Renal replacement therapy (RRT) is an important component in the care of critically ill children with acute kidney injury (AKI), inborn errors of metabolism, and certain intoxications that respond inadequately to conservative measures. There are several modalities of RRT including peritoneal dialysis (PD), continual flow peritoneal dialysis (CFPD), hemodialysis (HD), sustained low-efficiency dialysis (SLED), and continuous renal replacement therapy (CRRT). Each of these modalities has its own inherent advantages and risks, and the clinical situation will help guide the most appropriate approach for the individual patient. Peritoneal dialysis allows for both solute clearance and ultrafiltration. However, PD is suboptimal therapy for patients with life-threatening hyperkalemia, severe volume overload, or intoxications that would benefit from rapid ultrafiltration or solute clearance. In those settings, intermittent HD would provide a more effective modality. CRRT is a common mode of RRT utilized in the pediatric intensive care unit. There are three primary forms of CRRT including continuous veno-venous hemofiltration (CVVH; convective clearance), continuous veno-venous hemodialysis (CVVHD; diffusive clearance), and continuous veno-venous hemodiafiltration (CVVHDF) which is a combination of convective (CVVH) and diffusive (CVVHD) clearance. CRRT is frequently used in conjunction with extracorporeal membrane oxygenation (ECMO) therapy. Sustained low-efficiency dialysis (SLED) represents a hybrid between HD and CRRT. Although it has been used commonly in adults for over two decades, there is very little experience in pediatrics. A sound understanding of the various forms of RRT and their use in critical illness is essential.