Since 1984, ZEKE (ZEro Kinetic Energy) spectroscopy has matured into a very high resolution spectroscopy for the study of cations, anions, and indirectly through these species, neutrals--including very short lived intermediates in chemical rections. It has even yielded the first direct spectroscopic data on elusive transition states of chemical reactions. This is the first book to describe ZEKE spectroscopy, a new high resolution spectroscopy of molecular ions, neutral short-lived intermediates, and other species. The author's approach is to use a minimum of equations and large numbers of figures to help the reader toward a basic understanding of the many unique concepts of this new form of spectroscopy and the new spectroscopic information that it provides. This book will be of interest to anyone interested in the spectroscopy of ions or neutrals, particularly short-lived neutrals, formed from these ions. It should also be of interest to reaction kineticists interested in the study of reactions involving such highly state selected species.