How participatory budgeting works, and what we do and do not know about it

Participatory budgeting is a process in which residents decide how to spend part of a public budget. It is widely associated with the Brazilian city of Porto Alegre, where it began in 1989, and has since spread to many cities around the world.

A typical cycle has four stages: residents propose projects, volunteers and officials turn the proposals into costed options, residents vote, and the authority commits to fund the winners. Variations include who can vote, how much money is on the table, and whether young people or non-citizens may take part.

What people claim: more engagement, better-targeted spending, and greater trust. What is less clear: evaluations vary in quality, and results depend heavily on design details such as how much money is genuinely under residents' control and how the process treats groups who rarely attend meetings.

Limits: a small pot of money can produce a large amount of enthusiasm without changing the big decisions.

A useful question to ask of any scheme: what share of the total budget is actually decided this way, and who turns up?