Over the past four decades polymers containing imide and benzimidazole groups (usually as building blocks of the polymer backbone) have attracted increasing interest of scientists engaged in fundamental research as well as that of companies looking into their application and commercialization. This situation will apparently continue in the future and justifies that from time to time reviews be published which sum up the current state of knowledge in this field. imide and benzimidazole groups may impart a variety of useful properties to polymers, e. g., thermal stability chain stiffness, crystallinity, mesogenic properties, photoreactivity etc. These lead to a broad variety of potential applications. This book attempts to give the reader the necessary background to understand the factors that influence thermally stability and solubility of polymers and control the way in which these structures are formed.