Developing countries, in particular those in the WAEMU Zone, are in dire need for financial resources to meet their rising infrastructure requirements in order to strengthen their production capacities and to implement the new multi-objective development plans. Concomitantly, they are structurally experiencing real difficulties in mobilizing domestic tax revenues, and most of these countries remain vulnerable to public debt crises. It is therefore necessary for these countries to resort to financing strategies that can make it possible to maintain the public debt on a sustainable path. Thus, this thesis focuses on the tryptic tax revenues mobilization - public debt - financing of the economy, in order to propose financing mechanisms that these countries can use, to both maintain their economic growth on a sustainable path as well as to keep their public debt sustainable. Chapter 2 examines the existence of a fiscal space in the WAEMU member States. The objective is to show that countries have the fiscal margin to mobilise additional tax resources to ensure the financing of the economy and development, without compromising the sustainability of their financial position or the stability of their economies. The results show that since 1980, the fiscal performance of the WAEMU countries has been sub-optimal. The optimal level of taxation that maximizes growth over the period 1980 − 2017 is 20.6% of GDP. Compared to the average tax rate of 12.6% of GDP over the period of study, there would be, an additional tax revenue not collected by tax administrations around 8.0 percent of GDP. Chapter 3 focuses on the investigation of the causes of the low mobilization of tax revenues in the WAEMU countries. The aim is to emphasise the role of institutional factors in explaining the inadequacy of the mobilization of tax revenues, alongside the structural determinants. The analysis shows that the low mobilization of tax revenues in the WAEMU is symptomatic of the regular political and socio-economic conflicts that persist in the region. In fact, tax revenues are increasing because strong institutions and democratization place greater constraints on the executive, better bureaucracy and good governance, increase respect for the rule of law, reduce corruption, establish a fiscal social contract between taxpayers and governments, in a context of greater political freedom and ethnic consolidation.Chapter 4 focuses on the analysis of the efficiency of the VAT system in WAEMU countries. VAT plays an important role in the mobilisation of government resources, and it seems useful to examine its effectiveness. Concretely, we first estimated the VAT gap for the Union countries, using a so-called “top-down approach”, then conducted an econometric analysis to identify country-specific determinants explaining the different levels of VAT performance. The results show that only half of potential VAT revenues are collected each year within the Union. This poor performance reflects, among other things, the functioning of tax administration (compliance gap) and tax policy choices (policy gap). VAT therefore constitutes a potential source of tax resources to be exploited. Chapter 5 shows that there is a strong interest for countries to rely on public-private partnerships (PPPs) as a financing tool for the economy, especially in a context of budgetary constraints. The analysis answers the following question: do PPPs consider an alternative source of funding for public infrastructure? Indeed, PPPs are more advantageous because they enable the sharing and management of associated risks, improve the quality and reduce the costs of providing public goods and services. Empirical evidence shows that the impact of PPP investments is significantly higher than that of pure public investments. It also shows that the positive impact of PPP investments strengthens economic growth, but that this effect remains conditioned by the level of debt. (...)