Semiconducting polymer composites are materials that, thanks to their favorable electrical and mechanical properties, lend themselves naturally to applications such as polymer solar cells, light-emitting diodes, transistors and bio-sensors. This book describes the principles and concepts of semiconducting polymer composites in general, addressing electrical conductivity, energy alignment at interfaces, morphology, energy transfer, percolation theory and processing techniques. It also explores two different types of composites: mixtures of semiconducting and insulating or semiconducting and semiconducting polymers, respectively.