Microreactors as a novel concept in chemical technology enable the introduction of new reaction procedures in chemistry, molecular biology and pharmaceutical chemistry. Today, microreactors are realized as miniaturized continuous flow systems or reaction vessels with typical channel or chamber widths in the range of 10-500 mu m. The reduction of characteristic dimensions resulting in a small volume of the reaction tone allows an application of high temperature or reactant concentration gradients, as well as a significantly enhanced process control and heat management. Thereby, the unique advantages of microreaction systems are to carry out chemical reactions in unusual process regimes or under isothermal conditions. In addition, microreactors offer the production of toxic or explosive chemicals onsite or ondemand with an inherent safety. Recently, microreactors gain more and more relevance in process development and industrial research. One example for a successful application is the synthesis of a vitamin precursor by a homogeneously catalyzed liquid/liquid-phase reaction. Some other classes of chemical reactions, e.g. gas phase reactions (formation of ethylene oxide) or two phase systems (gas/liquid), are under investigation.