Collagens and proteins with collagen-like domains form large superfamilies in various species, and the numbers of known family members are increasing constantly. Vertebrates have at least 27 collagen types with 42 distinct polypeptide chains, >20 additional proteins with collagen-like domains and ∼20 isoenzymes of various collagen-modifying enzymes. Caenorhabditis elegans has ∼175 cuticle collagen polypeptides and two basement membrane collagens. Drosophila melanogaster has far fewer collagens than many other species but has ∼20 polypeptides similar to the catalytic subunits of prolyl 4-hydroxylase, the key enzyme of collagen synthesis. More than 1300 mutations have so far been characterized in 23 of the 42 human collagen genes in various diseases, and many mouse models and C. elegans mutants are also available to analyse the collagen gene family and their modifying enzymes.