Given the ubiquity of the ⍺-helix in the proteome, there has been much research in developing mimics of ⍺-helices, and most of this study has been toward developing proteinprotein interaction inhibitors. A common strategy for mimicking ⍺-helices has been through the use of constrained, helical peptides. The addition of a constraint typically provides for conformational and proteolytic stability and, in some cases, cell permeability. Some of the most well-known strategies included are lactam formation and hydrocarbon "stapling." Beyond those strategies, there have been many recent advances in developing constrained peptides. The purpose of this review is to highlight recent advances in the development of new helix-stabilizing technologies, constraint diversification strategies, tether diversification strategies, and combination strategies that create new bicyclic helical peptides. K E Y W O R D S alpha helix, helical peptides, peptide chemistry, protein-protein interactions 1 | INTRODUCTIONThere are a multitude of protein-protein interactions in the cell that are mediated by ⍺-helices, and in many disease states it would be advantageous to mimic features of an ⍺-helix with a small molecule or peptide. A common strategy for mimicking ⍺-helices has been through the use of constrained, helical peptides. 1-9 Doing so provides for conformational stability by reducing the number of degrees of freedom of the peptide and/or by facilitating ⍺-helical hydrogen bonding. This strategy also often provides for proteolytic stability: many proteases recognize an extended peptide conformation, but because of the conformational rigidity imparted by the constraint, helical peptides are not readily recognized by proteases that otherwise might recognize an Med Res Rev. 2019;39:749-770.wileyonlinelibrary.com/journal/med