13 October 2023, PhD defense, Simon Rey

The past 40 to 50 years have seen the rise of a wide range of innovative tools developed to deepen and renew the democratic process. One such tool is participatory budgeting (PB), which encompasses a large range of mechanisms that aim at making budgeting decisions in a participatory and collective manner. This thesis studies PB mechanisms. We view them as ways of obtaining a collective budgeting decision. More specifically, we investigate PB as a voting procedure in which citizens are asked to submit their preferences in order to decide which projects should be funded, subject to a budget constraint. Throughout the thesis, we define new fairness criteria to assess the outcome of PB processes; we develop a novel epistemic approach to PB; we present intricate ways to incorporate additional constraints into the formal analysis; we analyse the temporal aspects of PB; and finally, we study a multi-stage model. The end product covers a large diversity of implementations of PB processes, studied from various angles. I hope that this work, at its small scale, can help make better decisions for PB, and by that, improve the democratic process at a larger scale.