Collagen and elastin are fibrous proteins found in the extracellular matrix that provide structure. Collagen is the most abundant protein in the body and forms rope-like triple helices from three polypeptide chains. There are over 25 types of collagen that form fibrils, networks, or are associated with fibrils. Collagen synthesis involves post-translational modifications before assembly into fibers and crosslinking outside cells. Abnormalities in collagen synthesis and structure can cause disorders like Ehlers-Danlos syndrome and osteogenesis imperfecta.