Capillary electrophoresis (CE) is a small-scale separation technique based on differences in migration speed of species or compounds in an externally applied electric field. The separation takes place inside a capillary of which the internal diameter is typically situated between 50 and 100 µm. It is a very versatile technique with possible applications in a variety of fields. This editorial piece highlights one particular application that shows the potential of CE in monitoring or performing reactions. CE is not only used to analyse and follow-up enzymatic or chemical reactions in an off-line mode; the reaction can also be performed inside the capillary (i.e., in-line, whereby the reaction products formed are analysed in the same capillary). In this way, an integrated set-up is obtained which allows a higher degree of automation in analytical systems.