Abstract: This paper shows that a significant part of measured total factor productivity (TFP) differ- ences across countries is attributable not to technological factors that affect the entire economy neutrally, but rather, to variations in the structural composition of economies. In particular, the allocation of scarce inputs between agriculture and non-agriculture is important. We pro- vide a framework which maps the composition of the economy to measured aggregate TFP. A decomposition analysis suggests that as much as 85 percent of the international variation in TFP can be attributed to the composition of output. Estimation exercises indicate that recent findings of the conduciveness of good institutions, and, to some extent trade, on levels of TFP, may be thus explained.