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European cities are experiencing a triple phenomenon of vacancy (housing, office buildings, brownfields). Initially a symptom of “shrinking cities” and fuelling speculation, these spaces have become during the 1990s and the 2000s, the resources for forms of re-appropriation both by the citizens and by the local authorities. This comparative paper examines the case of two experiments of self-managed sites allowed by public actors - respectively a self-managed social centre and a fablab - in Madrid and Ghent. Highlighting the conditions under which these experiments were born, the article first shows how instrumentation by the urban project facilitates the opening of flexible modes of governance and implementation. In addition, despite powerful control of these spaces by public actors, the paper shows that targets and citizens can re-appropriate or skirt constraints, and divert resources. Demonstrating the non-exclusive dimension of the processes of de-territorialization, territorialization and re-territorialization that overlap, the article shows that any “territoriality regime” is hybrid. Finally, through this comparison, the article addresses the issue of policy circulation and its effects: while European urban policies produce standardization, the analysis of their implementation and of the behaviors of the users reveals processes of differentiation.