As new political institutions provide Brazilians with unprecedented access to policymaking and decisionmaking venues, politicians and activists have undertaken reform efforts to promote institutional arrangements partly designed to expand accountability. The expansion of participatory decisionmaking venues may grant citizens greater authority, but these institutions could also undermine municipal councils' ability to curb the prerogatives of mayors. This article analyzes participatory budgeting in São Paulo, Recife, and Porto Alegre to illustrate that mayors have differing capacities to implement their policy preferences, and this greatly affects how accountability may be extended.