This paper investigates the potential rupture that the United Kingdom's "Brexit" referendum of June 23, 2016, might bring about in intra-European Union youth mobilities, with a specific focus on the London region. In many respects, and counter-intuitively given the Brexit result, London has already become a "Eurocity": a magnet for young people, both highly educated and less educated, from all over Europe who, especially since the turn of the millennium, have flocked to the city and its wider region to work, study, and play. Now, these erstwhile open-ended migration trajectories have been potentially disrupted by a referendum result that few anticipated, and whose consequential results are still unclear. The main theoretical props for our analysis are the notions of "liquid migration," "tactics of belonging," "whiteness," "privilege," and "affect." Data are drawn from 60 in-depth interviews with Irish, Italian, and Romanian young-adult students and higher and lower skilled workers, carried out in late 2015 and early 2016, plus 27 reinterviews carried out in late 2016, post-Brexit. Results indicate participants' profound and generally negative reaction to Brexit and, as a consequence, a diversity of uncertainties and of plans over their future mobility: either to stay put using "tactics of belonging," or to return home earlier than planned, or to move on to another country. Finally, we find evidence that new hierarchies and boundaries are drawn between intra-European Union migrants as a result of Brexit. (Engbersen & Snel, 2013). We find these constitutive elements of liquid migration attractive for our study of contemporary youth migration within Europe, although some of our findings suggest that flexibility, openness to opportunities, and the search for security are more realistic characteristics of migrant motivations and behaviour than "intentional unpredictability."In the literature on youth life-course transitions, two concepts are important for our analysis in this paper. On the one hand, the "inclination to constant change" referred to in Bauman's quote above is advanced by Worth's (2009) notion of youth and young-adulthood as a continuous process of "becoming": we see this as more relevant and appropriate to our analysis than the traditional practice of agedefined life stages. On the other hand, the reality of sudden changes due to "fragility and vulnerability" (Bauman again) is nicely highlighted in the term "rupture" (Hörschelmann, 2011). Taken together, the notions of "rupture" and "becomings," combined with the framework of liquid migration, constitute a useful conceptual toolkit for understanding the social and spatial mobilities of young European Union (EU) citizens, both before and after the referendum of June 23, 2016, which saw 51.9% vote "leave" and 48.1% "remain."According to Bauman (2000, p. x), the key to the puzzle of liquid modernity is the premise that the "liquidity versus solidity conundrum"is not a dichotomy but that both conditions should be seen and treated as a couple "lock...