The development of organic light emitting diode (OLED) from its discovery in the Kodak Research Laboratories in the late 1970's to its commercialization for display applications in recent years will be described in this talk.  Several key ideas underlying the core of the science and technology will be highlighted, including the organic hetero-junction diode structure, the guest-host dopant scheme, the high-efficiency phosphorescent emitters, and the formation of ohmic organic/metal contacts.  Recent progress in OLED and challenges in developing OLED displays will also be discussed.