This article deals with the implementation of cross-sectoral programmes for urban regeneration. Contributing to the literature on social mixing in housing and to debates within the third generation implementation research, it argues that concepts of governing and implementing should be differentiated. Based on a case study of a cross-sectoral, multi-layered and multi-actor programme for urban regeneration of low-income neighbourhoods in Paris, it shows that governing relates to ‘power over’ a multidimensional policy problem, while implementing corresponds to ‘power to’ take action in a certain policy sector. This conceptual distinction allows the scrutiny of vertical and horizontal governance structures within cross-sectoral urban programmes, showing the complexity of integrated housing initiatives. Following Matland’s synthesis, the article argues that his variables of ambiguity and conflict cannot be isolated from one another. Indeed, the level of ambiguity around initial policy goals produces a proportional degree of conflict during the implementation phase.