This lecture covers the emission mechanisms in OLEDs, including fluorescence, phosphorescence, and TADF, explaining the differences in efficiency and materials used. It also delves into the basic operation principles and device architectures of OLEDs, discussing topics such as charge injection, conjugation, and bandgap engineering. The presentation further explores light extraction techniques, driving methods for OLED displays, and the main applications of OLED technology in signage, lighting, and automotive industries. Additionally, it addresses the challenges related to device degradation, lifetime, and large-area OLED production.