The principal subunits of the voltage-gated Na+, Ca2+ and K+ channels are members of a related gene family and are functionally autonomous in voltage-dependent activation, ion conductance and inactivation. In this article, recent work locating the structural elements that are responsible for these three basic functions of the voltage-gated ion channels is reviewed. These studies reveal strong functional analogies among the different ion channels and suggest that the striking differences in their properties arise as variations on a common structural and functional theme.