A theory of auroral kilometric radiation due to the nonlinear interaction between negative energy electromagnetic waves and coherent electrostatic ion cyclotron waves is developed. The theory predicts that such radiation produced must have X mode polarization and must have a frequency that lies in a narrow band between the right-hand cutoff and the Doppler-shifted beam cyclotron frequency for each local point of origin. The basic requirement for free space accessibility is the presence of high-energy beams in the inverted V events and a density-depleted cavity of the type observed by Isis 1 measurements. Beam densities of the order of 10-3 of the (depleted) background density appear to be necessary for the instability producing the radiation. Under ideal conditions, paths of wave growth of the order of 100 km may be adequate to produce observed radiation levels from electromagnetic noise at the appropriate frequency in the source region.