Glycosaminoglycans are polysaccharides containing alternating residues of uronic acid and amine derivatives of hexoses (such as N-acetylglucosamine). Typically the repeating unit carries a carboxyl group and often one or more sulfates, so that most glycosaminoglycans have a high density of negative charges. Glycosaminoglycans are often combined with protein to form proteoglycans and are an important component of the extracellular matrix of vertebrates.

Glycosaminoglycans provide structural support in vertebrates. Several glycosaminoglycans are listed in the following table.

Chondroitin sulfates	Hyaluronic Acid
Keratan sulfates	Heparin
Dermatan sulfates	Peptidoglycans

Glycosaminoglycans are sometimes called mucopolysaccharides.