Organic light-emitting device (OLED) technology shows tremendous commercial applications in communication, information, display, and lighting. It has been one of the most attractive projects in optoelectronic information field over the last decade. However, the internal efficiency is quite different from the external efficiency, and to some extent, a low external efficiency restrictes the development and application of OLEDs. The light out-coupling has been improved by a number of different techniques through the modification of device architecture. In this paper we present various light out-coupling techniques that have been implemented to enhance the external efficiency of OLEDs. Various OLED device modification techniques, e.g., micro-lens array, photonic crystal structure, nano-patterned and nanoporous films, and microcavity technique, have been reviewed and discussed. Finally, some perspectives on light out-coupling techniques are proposed.