Collagen is the backbone of connective tissue, which forms the soft skeleton that defines the body and much more. The various forms of healthy collagen and their normal formations are described. Connective tissue diseases are then described. Collagen supplementation is addressed: No, supplemental collagen precursors are not helpful in collagen-based connective tissue diseases; yes, supplemental mature collagen from other sources seems to be very helpful. This chapter concludes with a discussion of collagen and EDS/hypermobility.