The recent rise in world oil prices, coupled with heightened interest in the abatement of greenhouse gas emissions, has led to a sharp increase in domestic biofuels production around the world. Previous authors have devoted considerable attention to the impacts of these policies on a country-by-country basis. However, there are also strong interactions among these programs, as they compete in world markets for feedstocks and ultimately for a limited supply of global land. In this paper, we evaluate the interplay between two of the largest biofuels programs, namely the renewable fuel mandates in the US and the EU. We examine how the presence of each of these programs influences the other, and also how their combined impact influences global markets and land use around the world. We begin with an analysis of the origins of the recent bio-fuel boom, using the historical period from 2001-2006 for purposes of model validation. This was a period of rapidly rising oil prices, increased subsidies in the EU, and, in the US, there was a ban on the major competitor to ethanol for gasoline additives. Our analysis of this historical period permits us to evaluate the relative contribution of each of these factors to the global biofuel boom. We also use this historical simulation to establish a 2006 benchmark biofuel economy from which we conduct our analysis of future mandates. Our prospective analysis of the impacts of the biofuels boom on commodity markets focuses on the 2006-2015 time period, during which existing investments and new mandates in the US and EU are expected to substantially increase the share of agricultural products (e.g., corn in the US, oilseeds in the EU, and sugar in Brazil) utilized by the biofuels sector. In the US, this share could more than double from 2006 levels, while the share of oilseeds going to biodiesel in the EU could triple. Having established the baseline 2006-2015 scenario, we proceed to explore the interactions between the US and EU policies. This involves decomposing the contributions of each set of regional policies to the global changes in output and land use. The most dramatic interaction between the two sets of policies is for oilseed production in the US, where the sign of the output change is reversed in the presence of EU mandates (rising rather than falling). In other sectors, the interaction is more modest. However, when it comes to the impacts of these combined mandates on third economies, the two policies combine to have a much greater impact than just the US or just the EU policies alone.