The discovery of polymers with variable conductivity brought forth a paradigmatic change in chemistry and in other branches of science and technology. Electrochemistry has played a central role in the preparation, characterization and application of these new materials. This book is a systematic survey of the knowledge accumulated in this field in the last thirty years. It includes thermodynamic aspects, the theory of the mechanism of charge transport processes, the chemical and physical properties of these compounds, the techniques of characterization, the chemical and electrochemical methods of synthesis as well as the application of these systems. The book contains a compilation of the polymers prepared so far and covers the relevant literature.