Abstract: This paper sets up a model to account for differences in total factor productivity due to differences in enforcement of contracts. Vertical specialization generates the need for intra-period credit, because final goods producers cannot pay their intermediate goods suppliers before they produce their final good. The paper shows that if there are enforcement problems, the capital distribution is skewed in the sense that intermediate goods producers operate at lower capital levels and higher marginal products of capital than final goods producers. This wedge is created by the price for intermediate goods, which is lower in economies with bad enforcement. For this reason, the high-productivity firms in the intermediate goods sector have no incentive to grow and the low-productivity firms in the final goods sector, benefiting from low intermediate goods prices, have no incentive to shrink, which causes productivity to be lower in countries with bad enforcement. JEL classification: E10, E23 Key words: vertical specialization, limited enforcement, productivity 1 Introduction Why are certain countries poor and stay that way? The neoclassical growth model predicts that poor countries, even if living in autarky from the rest of the world, should rapidly catch up to industrialized countries. In the presence of perfect international capital markets this process would even take place instantaneously as capital flows to the countries with low capital endowment and high interest rates in order to equalize interest rates across countries. All this requires that technology across countries is identical. Prescott (1997) therefore raises the point that a theory explaining differences in production functions across nations, in particular differences in total factor productivity, is needed. This paper attempts to develop a theory of differences in TFP that have their origin in incomplete contract enforcement. We set up a dynamic general equilibrium model to examine the role played by incomplete enforcement of intra-period trade credit contracts. Output is produced in a sequence of intermediate production stages. Due to a benefit to specialization every firm concentrates its activity to the production of one single stage. Firms in each stage except the initial one purchase the intermediate good of the previous stage using trade credit and sell their output to the firms in the next stage, receiving trade credit of that firm in exchange. That is, rather than looking at enforcement problems pertaining to long term borrowing contracts we look at default risk within the chain of intra-period trade credit. A real world example for this chain of credit would be the two intermediate goods: iron ore and steel, and the final good automobiles. Iron ore is an input in the steel production and steel is an input in the automobile production. The model implicitly assumes that there is a benefit to specialization, that is, every firm in this economy specializes in only one sector of the economy. Car producers, therefore, would never buy iron ore to produce the steel themselves. Instead they purchase steel in the intermediate goods market. There is, by the way, plenty of evidence that vertical specialization in the real world is far more advanced than the relatively coarse grid of intermediate stages iron ore--steel--automobiles. Kei-Mu Yi (2001) shows that there is specialization even across countries that can account for the recent boost to international trade. He shows that effects of declines in tariffs are magnified if intermediate goods cross the border several times. Given that producers are even willing to pay tariffs by shipping goods across borders several times clearly indicates that there must be some payoff to specialization. Why do firms use trade credit? Notice that in a standard macro model with a sequence of intermediate goods as described above there would be no borrowing and lending other than potential long term borrowing contracts for financing of firms. …