Understanding the thermal conductivity of zinc oxide is of central importance in assessing its potential for a wide variety of applications in optoelectronics, power electronics and thermoelectric devices. Our single-crystal INS studies on LET demonstrate that we are able to model the one-phonon scattering using DFT and to measure the energy broadening from phonon-phonon scattering. Our powder INS studies on MARI reveal a red-shift in the multi-phonon scattering that is the signature of anharmonicity. We now propose to study the multi-phonon scattering by single-crystal INS using the MERLIN spectrometer. Our results will be the most direct test possible of the anharmonic corrections to the DFT. We expect to obtain a deeper understanding of anharmonicity in general, and the temperature dependence of the thermal conductivity of this technologically important material in particular.