This thesis aims at shading light on three issues which are at the forefront of the European Commission’s agenda. The first two chapters deal with the issue of state subsidies and their impact on market competition and development. Both papers design a theoretical setting where such impact can be assessed and provide for the tools needed for welfare analysis. The third chapter, instead, is mainly empirical and aims at measuring the effect on competition due to an increase in advertising in the context of public procurement auctions. Throughout this introduction, I will briefly describe the motivation and the main insights underlying each chapter.