Chitin, a linear long-chain biopolymer of β-(1,4)-linked N-acetylglucosamine (GlcNAc) residues, is the second most abundant polysaccharide in nature after cellulose and is found in fungal cell walls, insect exoskeletons and crustacean shells. Despite its abundance, chitin does not accrue in the environment due to the catalytic activity of chitinase enzymes. Chitinases belong to the glycosyl hydrolase superfamily (EC 3.2.1.x) and representatives are widespread, being produced by a variety of organisms including bacteria, fungi, plants, animals and humans. Chitinases play important roles in physiological processes such as parasitism, nutrition, morphogenesis and immunity. Notably, plant genomes often contain a large number of sequences that encode catalytically inactive chitinase family members that function as enzyme inhibitors or lectins. In addition to recognition of the potential industrial and agricultural uses of chitinases, there is an increasing demand for the products of chitinase catalytic activity for biotechnological and medical purposes. This mini-review summarises current understanding of the biochemistry of chitinases and describes some of their industrial, agricultural and pharmaceutical applications.