Book excerpt: This book explores the mechanism of alkali-metal ion/molecule association reaction, surveys the instrumental basis to study its kinetic, and describes the instrumentation to the measurement of alkali-metal ion affinities. The applications of the ion complexation mechanism in the condensed phase in reaction to direct analysis MS are also covered. Other topics include mechanism and reaction rate, experimental and theoretical ion affinities, applications of ion attachment reactions (IAR) to mass spectrometry such as alkali ion CIMS, ion attachment MS and cationization mass spectrometry of ESI, FAB, FD, LD, MALDI and SIMS and topics of IAR-based direct analysis mass spectrometry.