The Noise, Vibration and Harshness problem of gear rattle has recently become an important consideration of the automotive industry. Oscillations originating from the engine can cause the unselected, unloaded gears of the transmission to vibrate in and out of contact. Though much work has been published concerning the modelling of this behaviour, there is a lack of experimental studies to corroborate findings. The aim of this thesis is to investigate gear rattle using a dedicated experimental rig and, using the results obtained, develop a low-degree-of-freedom mathematical model of gear rattle.