The ω-helix is a modification of the α-helix. The α-helix has 3.6 residue in a single turn (3.6₁₃-helix), while the ω-helix (4.0₁₃-helix) has four residue per turn, although both are characterized by consecutive (i ¬ i +4) hydrogen bonds. Until now the ω-helix has been identified only in synthetic polypeptides of derivatives of aspartic acid and cysteine. However, recent analysis of The Protein Data Bank by a total least-squares method for fitting a helix to data points (called the HELFIT program) demonstrated that right-handed ω-helices actually occur in proteins. In this review we describe structural feature of ω-helices in synthetic polypeptides and proteins and address functional roles of many ω-helices identified in proteins including Chromobacterium violaceum phenylalanine hydroxylase.