This book reviews the current understanding of electronic, optical and magnetic properties of conjugated polymers in both the semiconducting and metallic states. It introduces in particular novel phenomena and concepts in these quasi- one-dimensional materials that differ from the well-established concepts valid for crystalline semiconductors. After a brief introductory chapter, the second chapter presents basic theore- tical concepts and treats in detail the various models for n-conjugated polymers and the computational methods required to derive observable quantities. Specific spatially...