This book comprehensively describes organic electronic devices developed in the past decades. It not only covers the mainstream devices including organic light emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic thin-film transistors (OTFTs) but also includes devices of recent interest such as organic immune transistors, organic phoatalysis devices, and themoelectrical devices. The book starts from the introduction of basic theory of organic semiconductor materials and devices, which acquaints the readers with the concepts of each type of device described in the following chapters. It also discusses the working principles, device layout, and fabrication process of these devices. The book is intended for undergraduate and postgraduate students who are interested in organic electronics, researchers/engineers working in the field of organic electronic devices/systems.