Complex glycans that are located at the surface of cells, deposited in the extracellular matrix and attached to soluble signalling molecules have a crucial role in the phenotypic expression of cellular genotypes. However, owing to their structural complexity and some redundancy in terms of structures that elicit a function, the therapeutic potential of complex glycans has not been well exploited, with a few notable exceptions. This review outlines recent advances that promise to increase our ability to use complex glycans as therapeutics. Opportunities for the development of further structure–function relationships for these complex molecules are also discussed.