Human chitinases (EC.126.96.36.199) are classified into family 18 of glycosyl hydrolase (GH18) superfamily based on their amino acid sequence similarities. Active chitinase hydrolyzes chitin, a β-1,4-linked N-acetyl-D-glucosamine oligosaccharide. Chitin is a major structural component of the insect exoskeletons and fungal cell walls, but is not found in vertebrates. In human, eight GH18 chitinases have been identified including active chitotriosidase and acidic mammalian chitinase. Most of the human chitinases lack chitinolytic activity due to mutation of an essential glutamic acid residue at the catalytic domain, and they are termed chitolectin. This review highlights some characteristics of human chitinases, compares structural differences among some human GH18 members, and discusses their cellular regulation and function. Finally, we summarize current views on the role of human chitinases in a variety of human diseases.