After the development of the tunable laser experimental studies in Rydberg states of atoms and molecules grew at a remarkable rate. Fundamental questions were resolved opening doors for more experimental activity and theoretical inquiry. In this comprehensive summary of knowledge of Rydberg states which was originally published in 1983 Professors Stebbings and Dunning brought together a select collection of experimental and theoretical discussions. Composed of works by the acknowledged leaders in the field this volume will be of value for anyone with an interest in molecular physics.