Peptide-amphiphiles, peptides to which a non-peptidic hydrophobic moiety has been added to the N or C terminal end, have been demonstrated to be a versatile method for simultaneously controlling nanostructure and chemical functionality. These amphiphiles are able to self-assemble, in a controlled fashion, into nanofibers with diameter between 6-10 nm and with length in excess of 1000 nm. At proper concentration these nanofibers form a viscoelastic gel capable of entrapping living cells and eliciting specific responses from them. Because of the flexibility of the display of chemical functionality on a controlled nanofibrous scaffold, applications for peptide-amphiphiles have been proposed including heterogeneous catalysis, nanoelectronics, drug delivery, and tissue engineering.