This book offers a wealth of knowledge and information about the fundamental and practical aspects of flexible organic light-emitting diode (OLED) devices. The book provides an overview of these devices by considering their merits and business potential, the history of their research and development, the fundamental technology, and required properties for materials, devices, processes, and future trends of flexible OLED devices. The practical sections describe novel, cutting-edge expertise for flexible substrates, gas barriers, encapsulation, novel electrodes, and on-demand patterning for OLED devices. Applications of the technologies of ultra-thin glass, stainless steel foil, and barrier films are described as flexible substrates. The book also explains features such as dry-barrier layers, wet-barrier layers, multi-layer barrier structures, dam-fill encapsulation, thin film encapsulation (TFE), and laminating encapsulation. In addition, there areexplanations of novel electrodes and on-demand ink-jet patterning, both of which are applicable to flexible OLED devices. As the novel electrodes, transparent conducting polymer, silver nanowire (AgNW), metal-mesh and roll-to-roll (R2R) process technologies are included. The know-how that is described here is applicable to flexible devices, not only for OLEDs, OPVs, OTFTs, and others but also for sensors, wearable devices, robots, and healthcare devices. The information contained in this valuable book is useful for all scientists, engineers, and managers who are interested in the field of flexible devices.