1. Introduction2. Fundamentals of Light Emission3. Electro- and Photo-luminescence from Organic Molecules4. Light Emitting Organic Semiconductors5. Charged Carrier Injection and Transport6. Carriers in Emitting Layer7. Paths toward High Quantum Efficiency from Emitting Molecule8. Device Optics9. Comparison and Differences between Organic LEDs and Inorganic LEDs10. Challenges for OLED Science11. Challenges for OLED Device Fabrication12. Blue, Green, Red, and White Light Emissions from Organic Molecules13. Comparison and Differences between Polymer OLEDs and Non-Polymer OLEDs14. Differences between Metallic OLEDs and Non-metallic OLEDs15. Thermally Activated Delayed Fluorescence in OLED16. OLED Operational Lifetimes and Degradation Mechanisms17. Impact of OLEDs on Science, Social and the World