The central aim of this thesis is to explain the weak participatory performance achieved by mechanisms of public participation in urban planning and management in the City of Buenos Aires. The analysis bears on the adoption by the Buenos Aires municipality of two participatory planning schemes modelled on initiatives successfully implemented in other urban settings: the Strategic Plan and the Participatory Budget. The theoretical foundations of the research rest on the assumption that the traditional scholarly literature on public participation in planning and development studies does not provide the analytical framework necessary to fully capture and understand the determinants of the `participatory performance' of initiatives of public engagement in urban policy-making. It is posited that the conceptual tools associated with the literature on `new institutional theory' offer an alternative theoretical perspective which is wellsuited to the analysis of the adoption and evolution of participatory planning schemes. New institutional theory has been consistently used to analyse and compare the economic performance of different institutional arrangements. The endeavour is to exploit its analytical potential to examine the performance of participatory planning mechanisms which are traditionally expected by the academic and development community to support a transition from purely electoral, representative forms of democracy towards `higher' modes of popular involvement in democratic decision-making. Strategic planning and participatory budgeting in Buenos Aires are examined through the analysis of two phases of institutional change: the first phase corresponds to the adoption of `foreign' planning models through institutional borrowing, whereas the second phase refers to the process of institutionalisation of these imported schemes in their host setting. This thesis seeks to contribute to the theoretical refinement of specific aspects of the literature on institutional change, and to assist policy-makers in enhancing the performance of the participatory planning mechanisms they choose to adopt.