Over the past two decades, microreactor technology has evolved to become a crucial component in the development of process intensification. Microreactors have helped to minimize reagent consumption and energy waste due to their small dimensions, which in most cases do not exceed 1 mm in at least one dimension. The small volume of microreactors enables safe handling of even hazardous or highly exothermic reactions while facilitating fast and easy parameter screening. As a consequence of the small size, the ratio of surface area to volume is much higher than in conventional reactors. This in turn affects other properties such as the flow regime, and mass and heat transfer. Because high pressure and temperature can be handled much easier at a very small scale, microreactors unlock new process windows. If a catalyst is deposited inside the microreactor in the form of a thin coating or a monolith, these devices may have great prospects in heterogeneous catalysis spanning from petrochemical to pharmaceutical applications. In this tutorial review, different methodologies to immobilize heterogeneous catalysts in microreactor structures have been collected, and applications for process development, data generation, and synthesis in continuous flow have been critically assessed. (C) 2017 Elsevier B.V. All rights reserved.