Over the past two decades collagen has grown into a large family of genetically distinct molecules, and the chatacteristic triple helical structure has also been shown to be present in several non-collagenous proteins. Details of the structure are now so refined that the mutation of a single glycine by cysteine has been shown to lead to a lethal form of a brittle bone disease. The chemistry of the polymerisation of the collagen molecules is now well established, although the additional cross-link reactions with increasing age are less clear. Some of these later reactions are non-enzymatic involving glucose, and are found to be accelerated in diabetics. However, the fundamental structure of collagen as a stable triple helix precisely polymerised into mechanically strong fibers provides the leather industry with its basic commodity, the food industry with a gel forming protein and the meat industry with the determining factor in the texture of meat. The quality of gelatin gels depends on the ability of the triple helix to reform, the kinetics of which in turn depend partly on the nature and location of the cross-links. Similarly, the texture of meat is determined by the strength of the small proportion of denatured collagen in meat following cooking, which again depends on the thermally stable cross-links. The biological diversity of collagenous structures and their varied functions in nature, as well as their role in the food and leather industries can now, to a large extent be explained, a far cry from the data available to the earliest collagen chemist, Henry Procter.