This paper examines the use of millichannels in designing multiphase reactors. We give a general analysis based on dimensionless numbers, followed by an illustration of this approach to catalytic packed-bed reactors. Finally, we discuss how such reactors can play an important role of increasing the number of electrocatalytic processes in the chemical industry. The increased degrees of freedom gives these reactors clear advantages over thermocatalytic non-structured reactors, as well as over electrocatalytic processes.