Biocatalysis has proven to be a useful supplementary technology for the chemical industry, allowing in some cases reactions which are not easily conducted by classical organic chemistry or in other cases allowing reactions which can replace several chemical steps. Highly chemo-, regio- and stereoselective bioconversions can simplify manufacturing processes to make them even more economically attractive and environmentally acceptable. The examples described are a selection of biocatalytic processes used for the preparation or modification of N-heterocycles.