Radio wave emission sources in the interplanetary medium (IPM) include type II and type III radio bursts and emission from planetary bow shock regions. The presence of electron beams in a range of energies suggests the possibility of a ring beam-plasma interaction as a mechanism for the generation of radio waves at both the fundamental and the second harmonic of the background electron plasma frequency. In this paper, ring beam-plasma interactions are simulated for the conditions of the IPM, &ohgr;e/&OHgr;e=100 to 200. In these simulations, the ring beam-plasma interaction couples the electrostatic Langmuir waves at the fundamental plasma frequency to electromagnetic waves; harmonic radiation is produced by an electrostatic trapped electron instability. Mode conversion processes permit the Z mode radiation generated through these instabilities to be converted to the X mode. Examination of both theory and observations suggests the ring beam-plasma interaction as a candidate for many of the radio phenomena in the IPM. ¿ American Geophysical Union 1996