introduces the fundamental aspects of defects in organic semiconductors and devices in relation to the structure of materials and architecture of electronic components. It covers the topics of defect formation and evolution, defect measurement techniques and their adaption to organic devices, the effects of defects on the physical properties of materials and their effects on the performance and lifetime of organic devices. Identifying defects and determining their characteristics in the structure of organic devices such as OLEDs, OFETs and OPVs make it possible to better understand degradation processes and develop solutions to improve the reliability of such devices. This book is intended for researchers and students in university programs or engineering schools who are specializing in electronics, energy and materials.