  Participatory budgeting is a democratic approach to deciding the funding of
public projects, which has been adopted in many cities across the world. We
present a survey of research on participatory budgeting emerging from the
computational social choice literature, which draws ideas from computer science
and microeconomic theory. We present a mathematical model for participatory
budgeting, which charts existing models across different axes including whether
the projects are treated as "divisible" or "indivisible" and whether there are
funding limits on individual projects. We then survey various approaches and
methods from the literature, giving special emphasis on issues of preference
elicitation, welfare objectives, fairness axioms, and voter incentives.
Finally, we discuss several directions in which research on participatory
budgeting can be extended in the future.
