Chemoenzymatic synthesis of glycans as an alternative to classical chemical synthesis has great interest for the exquisite sterospecificity and improved processivity and regioselectivity of the biological catalysts and for the possibility of using reagents less toxic for the environment. Nonetheless, the limitations intrinsic to the natural enzymes promoting sugar synthesis, namely glycoside hydrolases and glycosyltransferases, prompted efforts to engineer the former catalysts obtaining glycosynthases that catalyze the synthesis of oligo-, polysaccharides and glycoconjugates in quantitative yields and from cheap substrates. In this Chapter we show a survey of methods that, exploiting glycosidases and glycosynthases, allow the efficient and reliable preparation of glycans of synthetic relevance.