The present volume in this monograph series on Engineering Dielectrics is devoted to the subject of dielectric solids. The editors have decided to bifurcate Volume II into two parts, A and B, thereby taking into account the wide range of material encompassed by the subject. Herein, we present the contents of Volume IIA, which deals with the molecular structure and electrical behavior of solid insulating materials and systems. Volume IIB, which, hopefully, will appear within a year of the present volume, will treat the subject matter of measurement techniques that are used to evaluate and characterize insulating solids.