Résumé : In the three chapters of this PhD dissertation, I analyze the increase in the Belgian DI recipiency rate and the role of social security reforms in this phenomenon. The first chapter provides a general overview of the Belgian DI program, analyzes different possible explanations for its rapid growth between 2005 and 2015 and discusses different policy options to address this phenomenon. The second chapter studies the effects of monitoring the job-search activities exerted by the long-term unemployed population on their exit rate to employment, DI and other social safety net programs. The third chapter studies the effect of increasing the eligibility age for an old-age unemployment program, called Unemployment with Company Supplement (UCS), on workers’ employment rate and participation rate in DI or other social security programs.