Conjugated polymeric materials and their nanocomposites are widely used for the creation of alternative sources of renewable energy, cell phone screens, mobile gadgets, video players and OLED-TV, as well as organic diodes, transistors, sensors, etc. with field-dependent and spin-assisted electronic properties. Multifrequency EPR Spectroscopy methods can help researchers optimize their structural, magnetic and electronic properties for the creation of more efficient molecular devices. This book will acquaint the reader with the basic properties of conjugated polymers, the fundamentals of EPR Spectroscopy, and the information that can be obtained at different wavebands of EPR spectroscopy.