While Mayor Bertrand Delanoë had omitted the renovation of Les Halles in hisplans for the city in his 2001 inaugural address, in 2002, at the urging of theRATP and Espace Expansion, he decided to create a working group to undertakethis project during his tenure. Having made citizen participation a newgoal for local government, he also announced that the project would beundertaken with Parisians, especially local associations. The first part of thisarticle emphasizes the different postures that elected politicians, engineers,and experts have adopted over the course of forty years vis-à-vis the questionof citizen participation in urban planning. The second part explores the decision-making process for the Les Halles renovation over the last four years; itconsiders the issues and difficulties linked to the implementation of participatoryplans incorporating residents--whether they are members of localgroups or not--in complex urban planning projects.