This thesis is composed of four chapters on the relationship between Credit and Development Economics. In the first chapter we describe the concepts, relationships and mechanisms used in the other chapters. In the second chapter we evaluated the impact of reductions in three different financial constraints on GDP per capita in Brazil. To do so, we use a version of the neoclassical growth model with heterogeneous agents and three financial frictions. The model is calibrated for the Brazilian economy in 2009 and we do simulation exercises. In the first exercise, a reduction in the cost of participation in the credit market, which would allow the percentage of firms with credit in the economy to be equal to the average of the developed countries, would generate an increase in GDP per capita of 3.6 percent. In the second exercise, a reduction in the cost of monitoring, which would allow the spread in the economy to be equal to the average spread in developed countries, would generate a rise in GDP per capita of 1.7 percent. In the third exercise we evaluated a relaxation in the borrowing constraint. The results show that the reduction of collaterals in Brazil to the level of developed countries would raise GDP per capita by 12 percent. In the third chapter we seek to analyze the macroeconomic effects of the deepening of credit with free resources in Brazil in the period 2001-2011. In more specific terms, we evaluate the impacts of credit growth on GDP per capita. To do so, we used a version of the neoclassical growth model with heterogeneous agents, credit restrictions and occupational choice, calibrated for the Brazilian economy in 2001 and simulated in the model the increase in credit with free resources occurred in the period. In the exercise, the increase in free resources credit for firms from 10 percent in 2001 to 15 percent of GDP in 2011 generated a 1.5 percent increase in GDP per capita in the period. In the fourth chapter, our objective is to evaluate the impact of the increase of credit in Brazil in the period 2004-2008 on GDP per capita, using the model of Lloyd-Ellis and Bernhardt (2000). Thus we can compare the results of this model with the results of the model used in the third chapter. In the implementation of the model, we used a mixed approach of estimation and calibration for the Brazilian economy in 2004. In the exercise carried out, the increase in access to credit raised GDP per capita by 2 percent between 2004 and 2008.