This chapter describes the development, operation, and experimental results of the Third Generation JPL Electronic Nose (ENose), which operated on board the International Space Station (ISS) as a technology demonstration for seven months from 2008-2009. The JPL ENose is an array of chemiresistive sensors designed to monitor the environment for the sudden release of targeted chemical species, such as leaks or spills. The Third Generation JPL ENose was designed to detect, identify, and quantify eleven chemical species, three inorganic, ammonia, mercury, and sulfur dioxide, and eight organic compounds, which represent common classes of organic compounds such as alcohols, aromatics, and halocarbons. Chemical species were quantified at or below their 24 hour Spacecraft Maximum Allowable Concentrations (SMAC), generally in the parts-per-million range; some targeted species were detected in the parts-per-billion range. Analysis of third generation JPL ENose monitoring data on ISS show the short term presence of low concentrations of alcohols, octafluoropropane, and formaldehyde as well as frequent short term unknown events. Repeated unknown events were identified post-flight as sulfur hexafluoride.