An oligosaccharide is a saccharide polymer containing a small number (typically three to six) of component sugars, also known as simple sugars. They are generally found either O- or N-linked to compatible amino acid side chains in proteins or to lipid moieties.

In plants, animals, and single-cell eukaryotes

The basic structure is the same. These structures are synthesised onto asparagine residues on nascent proteins.