  Participatory budgeting is one of the exciting developments in deliberative
grassroots democracy. We concentrate on approval elections and propose
proportional representation axioms in participatory budgeting, by generalizing
relevant axioms for approval-based multi-winner elections. We observe a rich
landscape with respect to the computational complexity of identifying
proportional budgets and computing such, and present budgeting methods that
satisfy these axioms by identifying budgets that are representative to the
demands of vast segments of the voters.
