Hemodiafiltration (HDF) is an extracorporeal renal-replacement technique using a highly permeable membrane, in which diffusion and convection are conveniently combined to enhance solute removal in a wide spectrum of molecular weights. In this modality, ultrafiltration exceeds the desired fluid loss in the patient, and replacement fluid must be administered to achieve the target fluid balance. Over the years, various HDF variants have emerged, including acetate-free biofiltration, high-volume HDF, internal HDF, paired-filtration dialysis, middilution HDF, double high-flux HDF, push-pull HDF, and online HDF. Recent technology has allowed online production of large volumes of microbiologically ultrapure fluid for reinfusion, greatly simplifying the practice of HDF. Several advantages of HDF over purely diffusive hemodialysis techniques have been described in the literature, including a greater clearance of urea, phosphate, beta(2)-microglobulin and other larger solutes, reduction in dialysis hypotension, and improved anemia management. Although randomized controlled trials have failed to show a survival benefit of HDF, recent data from large observational studies suggest a positive effect of HDF on survival. This article provides a brief review of the history of HDF, the various HDF techniques, and summary of their clinical effects.