Peptides as short as 20 amino acid residues can form ion-conducting pores within lipid bilayers. Some of these peptides exhibit ion selectivity and can alter the pore size in response to changes in membrane potential. Artificial ion-channel peptides have been engineered by reverse-designing natural ion-channel proteins and peptides. Such artificial channels, capable of selective ion permeation across lipid membranes, are expected to serve as key functional components of molecular robots composed of liposomal units.