Since the first report in 1993 (JACS 115, 5887-5888) of a peptide able to form a monomeric beta-hairpin structure in aqueous solution, the design of peptides forming either beta-hairpins (two-stranded antiparallel beta-sheets) or three-stranded antiparallel beta-sheets has become a field of intense interest. These studies have yielded great insights into the principles governing the stability and folding of beta-hairpins and antiparallel beta-sheets. This chapter reviews briefly those principles and describes a protocol for the de novo design of beta-sheet-forming peptides based on them. Criteria to select appropriate turn and strand residues and to avoid aggregation are provided. Because nuclear magnetic resonance is the most appropriate technique to check the success of new designs, the nuclear magnetic resonance parameters characteristic of beta-hairpins and three-stranded antiparallel beta-sheets are given.