Microfabrication techniques are increasingly used in different fields of chemistry to realize structures with capabilities exceeding those of conventional macroscopic systems. In addition to already demonstrated chemical and biological analysis applications, microfabricated chemical systems are expected to have a number of advantages for chemical synthesis, chemical kinetics studies, and process development. Chemical processing advantages from increased heat and mass transfer in small dimensions are demonstrated with model gas, liquid, and multiphase reaction systems. These case studies also serve to illustrate benefits of integrating sensors for flow, temperature, and chemical composition with microfluidic reaction and control components. The role of reaction engineering in the development of microreaction technology is described along with new approaches to scale up based upon replication of microchemical devices.