The presentation shall give an overview about the developments of different solid electrolyte gas sensors for both, space and terrestrial applications. Special emphasis will be laid to the recently performed space experiment "FIPEX on ISS" for the measurement of the residual Earth atmosphere in about 300-400 km altitude. Further developments for medical and environmental control applications will also be introduced. Finally, sensor production and design issues, for which nanomaterials and -techniques become more and more important, are addressed.