Book excerpt: The use of silicon-based microsystems for chemical analysis is one of the most promising concepts in the recent developments in micro system technology (MST). It is expected that chemical sensors will be increasingly integrated in so-called miniaturized total analysis systems (muTAS), a concept first presented by Ciba-Geigy. In such systems, all steps in a chemical determination, from sampling to detection and data treatment, are integrated in one miniature instrument. muTAS offer a variety of advantages over conventional analysis systems such as improved analytical performance, reduced reagent and power consumption, small size, possibility of new and more complicated functions, higher reliability and lower fabrication costs. Application of muTAS may be found in fields like process industry, environmental monitoring, medical diagnostics, aeronautics, automotive industry, etc.