Use of model systems to explore the forces that control beta sheet formation was stymied for many years by the perception that small increments of beta sheet necessarily aggregate. Recently, however, a number of short peptides (9-16 residues in length) that fold into two-stranded antiparallel beta sheets ('beta hairpins') have been reported; several short peptides (20-24 residues in length) that fold into three-stranded antiparallel beta sheets have also been described. These model systems are beginning to provide fundamental insights into the origins of beta sheet conformational stability.