Photopatterning of organic photoresist is the standard tool for microstructuring in microelectronics. Therefore it is not surprising that in the field of micro- and nanosystem technology such a technique is also preferred for mass production. The top-down approach for getting microstructures in microsystems comprises UV-, X-ray-, electron-beam and ion-projection lithographical technologies. Problems are the demands for high aspect ratios and depth of focus, which can be solved by new lithographic tools or resists. To get functionalized structured surfaces the bottom-up approach for nanosystem technology also uses photostructuring methods for defined immobilization or deposition of supramolecular moieties to create defined surfaces. Functionalization of surfaces by immobilizing biomolecules covalently on reactive surface groups or in photostructured membranes lead to biosensors for analytical purposes. Miniaturized biosensors comprising the enzyme glucose oxidase are biosensors with the highest importance worldwide. However other techniques as microcontact printing or SPM techniques may be used for deposition and immobilization of organic molecules. Using micro- and nanostructure technology affinity assays, cell assays and DNA devices on chip can be realized for rapid screening purposes in future.