Recent advances in both experimental techniques and theoretical methodologies have meant that increasingly sophisticated studies concerning the formation, structures, energetics, and reaction dynamics of state- or energy-selected molecular ions can now be performed. In order to better serve the ion chemistry and physics community, each volume of this series will be dedicated to reviewing a specific topic, emphasizing new experimental and theoretical developments in the study of ions. This third volume is devoted to the study of unimolecular and bimolecular ionic processes. Special emphasis is given to studies related to planetary and interstellar ion chemistry and physics, the understanding of which has been a great impetus to the study of ion-molecule reactions. Each of the nine chapters making up this volume is written by a leading researcher in the respective field. This series will help stimulate new research directions and point to future opportunities in the fields of ion chemistry and physics.