Chronicles the development of ion mobility spectrometry (IMS) from its inception two decades ago to current applications and plans for the future. Fundamental aspects of atmospheric pressure ion processes and their chemical ionization effect on the response characteristics of IMS are analyzed. The theory and physics governing the motion of ions drifting through an atmospheric pressure buffer gas in an electric field are presented in a simplified yet comprehensive manner. The book also presents an up-to-date report on recent developments and applications in IMS instrumentation, including laboratory instruments, monitoring systems, and hand-held instrumentation. The performance of GC/ IMS is analyzed and critically evaluated, and tables of reliable reducer mobility values are provided.