This volume contains contributions written by eminent specialists which deal with various aspects of the structure and dynamics of non-rigid molecules. Together these papers provide an authoritative overview of research and progress in this field. The contents are divided into three sections which cover, respectively, Fundamental Questions in Non-Rigid Molecular Problems; the Structure and Symmetry of Non-Rigid Molecular Systems; and the Dynamics of Non-Rigid Molecular Systems. For researchers and graduate students of molecular physics and theoretical physics.