Abstract: Abstract: Mesoscale phenomena represent a common challenge in chemical engineering. This article reviews three decades of related research at IPE, CAS, spanning from the energy-minimization multiscale (EMMS) model specific for gas–solid fluidization to the EMMS principle, which is probably general for all mesoscale problems. This review focuses on elucidating the following questions: Why are mesoscale problems challenging? Is there a common governing principle for mesoscale behavior? Could a common principle allow more accurate and efficient simulation of chemical processes? Finally, the concept of mesoscience is discussed, based on the potential generality of the EMMS principle.