The paper reports preliminary results from an econometric model of world grains markets. The model is used to address the source of shocks (demand or supply?), the scale of their price impact (greater for corn than wheat) and the price impact of the growth of the use of corn as a biofuel feedstock (substantial for corn, less so for wheat). We also ask whether it makes sense to think of grains as a single composite commodity or whether idiosyncratic crop-specific factors remain important.