In micro-spaces, viscous force, surface tension, conduction heat transfer, and molecular diffusion become dominant. These features achievable in micro-spaces make it possible to handle highly exothermic and rapid reactions and to produce fine particles with narrow size distribution. The goal of our research is to develop a fundamental approach to design, operation, and control of microreactors. In the first half of this paper, three types of systematic design methods are explained. In the second half of this paper, the development of process monitoring system, which is applicable for effectively diagnosing faults such as blockage and catalyst deterioration in microreactors, is explained. Copyright © 2009 by ASME.