Since the Brexit referendum in June 2016, attention has focused on internal UK debates about leaving the EU. Yet potentially the most important outcome of the UK’s vote to leave is how it is driving significant change in the EU itself. Brexit has catalyzed debates across Europe that have been brewing for years, in part because of UK disengagement, and will assume greater prominence when the UK actually leaves, if that is indeed the outcome. These debates about the EU’s future are wide ranging. They include how the union will be rebalanced internally after the exit of one of its largest members; the bloc’s future role in a multipolar Europe with other non-EU European countries; and its positioning in a changing world outside the continent, especially in relation to global powers such as the US. Far from only Brexit defining the future of the EU, it is just one of several challenges and opportunities. How the EU responds, from pressures facing the eurozone and Schengen areas to ties with other world powers, will determine its future and place in the world, as well as framing its post-Brexit UK relationship. On the external front, numerous challenges are particularly pressing in Brussels in what European Council President Donald Tusk has called the EU’s new geopolitical reality. In 2017, he outlined these pressures, which include an increasingly assertive Russia and China; instability in the Middle East, which has driven migration problems; and policy uncertainty from Washington, with pro-Brexit Donald Trump calling for the EU"s further dismemberment. Wide-ranging as these threats are, Russia and the US are the two non-EU states that will probably be pivotal in shaping how Brexit plays out in relation to Europe’s changing landscape and the wider multipolar world. To be sure, other powers such as China will also have influence, but it will mainly be the choices of Washington and Moscow — whether to engage, exploit or ignore — that will shape the context in which Brexit unfolds. Russia knows it can gain from an increasingly fractured EU, not least as Vladimir Putin pushes the Eurasian Union as a countervailing power. Moreover, an emboldened Putin would now unquestionably welcome a prolonged post-Brexit period of introspection, with the EU forced to focus more on internal challenges and less on issues such as Ukraine, where Moscow and Brussels are at loggerheads. Given current tensions with Russia, it is the EU’s particular misfortune that the US president, who may be in the White House for another five years, has gone as far as to call the EU a “foe.” Andrew Hammond Given current tensions with Russia, it is the EU’s particular misfortune that the US president, who may be in the White House for another five years, has gone as far as to call the EU a “foe.” While Trump’s antipathy toward the bloc is broad-based, it is especially intense on the economic front because of Europe’s big goods trade surpluses with the US. This new geopolitical reality is already catalyzing the EU into reform, including a European Defence Action Plan. This advocates greater military cooperation between member states, and reversing about a decade of defense cuts. Externally, Brexit is also changing the relationship of Brussels with non-EU European countries, including Norway, Switzerland, Ukraine, Turkey, Lichtenstein and non-EU states in the Balkans. Each has developed relations with Brussels intended as a means to an end of eventual EU membership, or at least closer relations, but Brexit has injected greater uncertainty into these assumptions. For instance, there has been some discussion of whether Brexit might open opportunities for a more far-reaching overhaul of Europe’s institutional architecture beyond those ideas that already exist in “off-the-shelf models.” This includes an August 2016 think-tank proposal, focused on the future EU-UK relationship, which called for a new “continental partnership” in a relationship, short of EU membership, that went beyond a simple free trade deal. Such ideas have, however, at least temporarily lost momentum, partly because Brussels wants to change on its own terms and timeframes, and not be seen to dance to a Brexit tune and accommodate the departing UK. Nevertheless, such far-reaching reform may ultimately arrive if the UK Parliament ratifies a modified version of the vexed withdrawal agreement negotiated by Theresa May; there would then be growing need for the EU to think more creatively as the next wave of future relationship negotiations gets underway. Thus, significant change is now on the cards for the EU, from the complex array of challenges and opportunities it now faces, Brexit and beyond. How Brussels responds, which is not yet clear, will frame not just its future relationship with the UK, but also its broader place in the world at a time of geopolitical turbulence.