We examine the differential capacity of civil society organisations to represent the poor in institutional spaces for citizen participation in the city of Sao Paulo, Brazil. The data was produced by a unique survey of civil society actors who work for, or with, sectors of the lower-middle class, the working class, and the urban poor. Contrary to the focus on autonomy in much of the work on civil society, we find support for the claim that collective actors with relations to institutional actors, and the Workers' Party and State actors in particular, have the highest propensity to participate. We also find support for the idea that the institutional design of participatory policy-making spaces has a significant impact on who participates, and that this impact varies by type of civil society actor. We therefore suggest a polity perspective on civil society organisations that, unlike the more common civil society perspective, is sensitive to the differential capacity for action and to institutional effects.