The cover picture shows the structure of a β-peptide bundle protein whose stability was improved by optimizing salt-bridge interactions on the bundle surface. There is considerable current interest in the design of higher-order, non-proteinaceous assemblies possessing defined oligomeric states, as these have potential as nanomaterials and catalysts. We reported previously that certain β3-peptides self-assemble spontaneously in aqueous solution into discrete bundles of defined stoichiometry (β-peptide bundles) whose kinetic and thermodynamic metrics are virtually indistinguishable from those of natural proteins. Here we show that the stability of a β-peptide bundle can be tuned by controlling the length of a solvent-exposed surface salt-bridge interaction. Combined with previous work on the roles of internal packing residues, these results provide another critical step in the bottom-up assembly of β-peptides with defined sizes, reproducible structures, and sophisticated function. For more information see the paper by A. Schepartz, et al. on p. 1035 ff.