The book provides useful and updated information concerning multiple aspects of certain polymer types. These polymers are heterochain ones (polysiloxanes, polyazomethynes, polyaniline, polythiophene and polypyrrole, polyurethanes and polyimides) that can develop special or high performance properties of interest for advanced fields: electronics, optics, nanosciences, environmental protection, coatings, etc. The key aspects concerning synthesis and characterisation techniques, evaluation of their functionalities and main application directions are presented. One studied class of heterochain polymers consists in siloxane-containing polymers, besides other elements within the chain (N, P, B, and C). Their synthesis possibilities, as well as properties and functionalities in correlation with structures, are discussed. The most recent developments in liquid crystalline polymers of various architectures, containing siloxane segments in structure are reviewed, emphasising the role of Si-O bonds on their thermotropic and overall properties