Devices for gas detection and analysis are on the market for a variety of applications. Disadvantages of commonplace gas analysers are their high price, difficult operation and large size. Cheaper and smaller gas sensors and detectors measure concentrations accurately, but are limited to specific gases. To overcome these drawbacks of current technologies was the motivation to study a new type of miniaturised gas analyser. This work deals with gas ionization by micro discharges, and analysis by ion mobility. The first chapters give an overview of past research in the field. The involved physical theory is presented in a compilation of relevant subjects, from the basics of electrostatics to electrical breakdown in small gaps, and DC glow discharge. The components of an ion mobility spectrometer are studied with a focus on the ionizer. A series of miniature and micro ionizers were fabricated and used to examine micro discharges as such and as a means of ionization at atmospheric pressure. Factors that affect resolution and stability of micro ion mobility spectrometers are discussed. This book is a valuable resource for anyone interested in micro discharges and ionization.