Light emitting field effect transistors based on molecular and polymeric organic semiconductors are multifunctional devices that integrate light emission with the current modulating function of a transistor The planar geometry of organic light emitting field effect transistors (OLEFETs) offers direct access to the light emission region, providing a I unique experimental configuration to investigate fundamental optical and electronic properties in organic semiconductors. OLEFETs show great potential for technological applications such as active matrix full color electroluminescent displays. In this Feature Article we review advances in OLEFETs since their first demonstration in 2003 and we highlight exciting challenges associated with their future development.