The fabrication, characterization and application of polyimide-based flexible microelectrodes for recording from and stimulation of biological tissue are described. The planar electrodes consist of a polyimide-platinum-polyimide sandwich structure with a total thickness of 10 to 40 mum fabricated on Pyrex or silicon wafers. Several designs with mono-polar or multi-polar probe-type electrodes have been realized. Two different fabrication technologies. photosensitive (PS-PI) and non-photosensitive polyimide (NPS- PI) have been developed. For the photostructurable polyimide 2 three-mask process was realized, whereas for the non-photosensitive polyimide a simpler two-mask process using dry etching techniques was used. A sacrificial layer of aluminum served for detachment of the structures by anodic metal dissolution. This is a particularly biocompatible release procedure as the microelectrodes are detached from the fabrication substrate in a sodium salt solution. Obtained microelectrodes were characterized by impedance spectroscopy and were used to record multi-channel EMG signals from free-walking insects.