The real impact of taxes on the economy can only be assessed when we consider the behavioral responses of economic agents due to these taxes. Two kinds of responses are studied in this thesis: changes in organizational form and location choices. The first part of this study shows how income taxation in Brazil gives incentives to some classes of taxpayers to incorporate in order to reduce their tax burden. Microdata on these taxpayers indicate that the probability of incorporation is strongly related to tax rules. The second part of the study uses the case of two cities engaged in fiscal competition in order to measure the sensitivity of firm s location choices to municipal tax rates. Firm data show that these two cities, located in the greater São Paulo area, were able to attract a large number of firms to their territory. However, data from firms surveys indicate that the number of jobs did not grow accordingly. In both cases studied, there are evidences that firms change their behaviour with the main objective of avoiding taxes.