The purpose of this thesis is to identify practices of fiscal management within corporate groups in Tunisia to assess the impact of these practices on fiscal performance of these major players in the Tunisian economy. Thus, the first chapter is devoted to the definition of the concept of group of companies in Tunisia highlighting their economic weight and emphasizing their legal reality. The second chapter focuses on the identification of different fiscal management practices that use these groups through an analysis of fiscal jurisprudence represented by 17 judgments of the Court of Cassation from 2005 to 2011. A survey conducted among managers of parent companies listed on the TSE is also mobilized during this chapter to sound the reasons for the non-application of the tax consolidation regime however supposed to be an effective tax planning tool. The third chapter introduces the theory of transaction costs that seems adequate to detect the relationship between fiscal management practices and fiscal performance. This relationship is developed through three research hypotheses that are forecasting the type of correlation between intra-group transactions, intra-group debt and financial relief on one side, and the effective tax rate on the other (respectively H1, H2 et H3). These hypotheses are tested in a fourth and last chapter through a multivariate statistical analysis conducted on financial data from a sample of 36 groups of companies (21 non-financial groups and 15 financial companies), whose parent company is listed on the TSE over a period from 2007 to 2011. So this statistical analysis led to confirm two of the three research hypotheses (H1 and H3) in the whole sample and in the financial sector and a single hypothesis in the non-financial sector (H3). It was then found that Tunisian groups of companies operate mainly through two practices to reduce their effective tax rate: financial relief and intra-group transactions practices (this last practice has been verified only in the financial sector).