Among the different methods of incrementing the transdermal absorption of drugs, iontophoresis has been the focus of considerable research. The fundamental s of iontophoresis are presented in this chapter along with the factors that need to be considered in order to apply this technique effectively (i.e. current density, ionic strength, and pH). The main applications of iontophoresis for the topical and systemic delivery of drugs are also discussed. Finally, the usefulness of reverse iontophoresis is addressed.