In this review, we have collected and analysed collagen glycosylation data in an effort to better understand its possible function in fibrillogenesis. Towards that end, we have identified glycosylation sites in many different fibril-forming collagen molecules (Types I, II, III, V, XI and XXIV) and, more importantly, the glycan itself as well as the percentage of collagen molecules in the sample that contain it. As the numbers of quantitative analyses of different collagen types from different species and tissues taken under different physiological conditions grows, a more accurate picture is emerging of the role that collagen O-glycosylation may play in fibrillogenesis. It is becoming increasingly clear that glycosylation does play an important part in the initial stages of the axial assembly of collagen molecules as well as in the lateral control of fibril size. Much remains unknown of the precise mechanisms involved, however, and further detailed analyses will be required before a complete picture of the various in vivo roles played by the glycans emerges.