Peptide nanocoatings with tailored surface-wetting properties were formed on a range of organic (cellulose and cotton) and inorganic (glass) substrates via surface-initiated ring-opening polymerization of amino acid N-carboxyanhydride derivatives. The film thickness, surface roughness, and wettability can be tuned by controlling the polymerization time and the type of N-carboxyanhydride derivative used (i.e. lysine or valine). Whereas poly(l-lysine) coatings are hydrophilic, poly(l-valine) coatings exhibit water-repellent properties. The functional polypeptide nanocoatings can potentially be applied to waterproof woven fabrics, macromolecular separation technologies, biodiagnostic sensors, and sustained drug-release wound dressings.