Non-natural folded polymers (foldamers) display considerable versatility, and the design of such molecules is of great current interest. In this respect, peptidic foldamers are perhaps the best-characterized systems, as they populate a number of residue-controlled secondary structures, which have found various biological applications and have also led to the creation of nanostructured materials. This critical review covers recent developments related to diverse building blocks and modern foldamer design principles, such as the stereochemical patterning methods. The recent achievements concerning tertiary/quaternary structures and the self-assembling foldameric nanostructures are also addressed (176 references).