The applications of organic semiconductors are driven by their unique physical properties- notably, weak intermolecular bonds which facilitate heterogeneous materials integration but also promote disorder and localization. This book addresses traditional applications of organic semiconductors, such as thin-film transistors, light-emitting devices and solar cells, as well as promising research areas like spintronics, strong coupling and polaritons. The focus is on elucidating the physics of organic semiconductors and exploiting the physics to improve device formation.