The evolution of hemodiafi ltration (HDF) has become possible by the advances in the construction of dialysis membranes. The availability of a high-fl ux membrane, partially hydrophilic with high sieving coeffi cients and a reduced wall thickness has made it possible to conveniently combine diffusion and convection for blood purifi cation. The second important step has been the development of accurate ultrafi ltration control systems. Machines capable of managing large amounts of fl uid turnover allowed safe and effective HDF. Some new dialysis machines are specifi cally designed to perform HDF with adequate embedded software. The third step regards the production of large amounts of ultrapure dialysate and replacement fl uid. For years replacement fl uid was produced in bags, while recently, online production has enabled high volume exchanges in HDF. All these advances, together with the creativity of several groups, have spurred new interest in HDF and have led to the development of various HDF techniques, which are successfully applied to uremic patients with important clinical benefi ts.