Biocatalysis has widened its scope and relevance with the availability of new molecular tools, e.g. improved expression systems, protein and metabolic engineering, and rational immobilization techniques. However, applications are still hampered by low productivity and scale-up difficulties. A practical step to improve biocatalyst (enzymes, whole-cells) performance is to use flow reactors. In a recent review published in Trends in Biotechnology, Pedro Fernandes from BERG-iBB together with colleagues from the Universities of Milan and Nottingham describe the state of the art on the design and use of biocatalysis in flow reactors. The successes of the technology, new opportunities, problems and advances are critically discussed. Click on title to learn more.