Electronic and optoelectronic devices using organic materials as active elements are attractive because they can take advantage of organic materials. Among them, organic field-effect transistors (OFETs), which consist of organic semiconductors, dielectric layers, and electrodes, are expected to be a promising technology for application in displays, sensors and memories. Organic semiconductors play a key role in determining the device characteristics. Recent technological advances in OFETs have triggered intensive research into molecular design, synthesis, device fabrication, thin film morphology and transport of holes and electrons. This book presents and discusses research on new organic semiconductors.