The volumetric, uniform, and selective heating of microwaves is a novel technique with the potential to be established in a wide range of applications. The individual interaction of each phase/component of multiphase/multicomponent systems with microwaves creates more than a temperature in the system. Having a high local temperature on an active site that is a strong microwave receptor promotes catalytic and non-catalytic reactions. The relatively low temperature of the bulk material(s) restricts the undesirable secondary reactions correspondingly. This finding has already led to several applications. In this work, the fundamentals of microwave heating and their prospective applications are debated. Select lab-scale results of metal and sulphur removal from petroleum oil, pyrolysis of lignin, and dry reforming of methane are demonstrated. The expected impacts of microwaves on other multiphase reactions are proposed.