Oligosaccharide synthesis is becoming increasingly important to the pharmaceutical industry because these biomolecules have potential application as therapeutics. Enzymatic synthesis of oligosaccharides includes both glycosyl transferases and glycosidases. The main advantage of this approach compared with traditional chemical synthesis is the regio- and stereo-selectivity that can be achieved without the need for protecting functional groups. However, the limited availability of glycosyl transferases, the high cost of their substrates, and the poor yields of the synthetic reactions performed by the glycosidases hamper their use in the large-scale production of oligosaccharides. The recent advent of glycosynthases - specifically mutated glycosidases that efficiently synthesize oligosaccharides but do not hydrolyse them - represents a promising solution to these problems. Here, we review the most recent developments in the glycosynthase approach.