Within the current asylum-immigration scenario in Europe, there is an increasing amount of “intractable situations” related to the institutional management of people who reside in a country but are not supposed to be there. These are not only undocumented people, but a wide varied of mobile asylum seekers, Dubliners, rejected, appealing and non-returnable subjects who fall out of the census. This is the case of mobile populations in transit zones, such as Calais and Ventimiglia, but also in urban spaces. While requiring solutions (in terms of assistance and regulation), these situations cannot be legally administered, as they emerge in the grey zones of law and reality: here is where a universe of different social actors come into play. Even those, who by definition are against institutions, such as anarchist actors of squatting housing movements (Mudu and Chattopadhyay, 2016). Drawing from ethnographic research among migrants, squatters and civil society in Amsterdam, this paper illustrates that these non-institutional actors are functional to manage – and in a way also to control – the intractable issues created by the overlapping of several layers of legal and administrative regulations over migration and citizenship. After analysing the institutional grey zone experienced by most of the undocumented people I met in Amsterdam, I describe the shifting interactions (characterised by solidarity and tensions) between different groups of migrants and squatters through the lens of “interstices” (Fontanari, Ambrosini, 2018). While the collaboration between supporters and undocumented migrants opens up spaces of urban citizenship (Baubock, 2003), drawing from migrants’ life histories I consider to what extent these spaces can produce innovative solutions to intractable problems or a long-lasting marginality. This paper aims to contribute to debates about the right to the city and housing, informal refugee reception and the pitfalls of asylum and migration regulations in Europe.