The EU's remaining 27 members will have to weigh their own potential losses after the U.K voted for Brexit, with a few countries in particular facing much greater stakes.
This group includes two Mediterranean holiday spots (Malta and Cyprus), a next-door neighbor (Ireland), as well as countries whose job-seeking citizens have been attracted to the U.K. labor market in recent years (Poland and Lithuania). These countries heavily rely on the U.K. both in terms of trade and tourism.
The U.K.'s trade with the EU, which according to the IMF was worth over $500 billion in 2015, will likely be the single-most important issue as it prepares to negotiate its exit.
While they could decide to follow the example set by Switzerland and Norway and opt for membership in the European Free Trade Association, required payments into the EU budget may prove a sticking point for Eurosceptic British lawmakers. Even so, the sheer scale of bilateral trade with the likes of Germany ($137 billion last year) and the Netherlands ($73 billion) means there will be a lot of pressure to find common ground in terms of trade.
When considering which EU countries have the most to lose on a relative basis, Germany is closer to the middle of the pack, with the U.K. representing 5.8 percent of its global trade flows. It's a bigger deal for the likes of Belgium (closer to 7 percent), Cyprus (almost 8 percent), and neighboring Ireland (18.6 percent), which ranked first in S&P's recently-published 'Brexit Sensitivity Index'.
Ireland is also particularly vulnerable to any travel restrictions that could arise as a result of Brexit, which must happen within two years of activating Article 50 of the Lisbon Treaty. In 2014, U.K. visitors were responsible for 14 percent of all tourism spending, or almost 900 million euros, according to Eurostat data.
Two Mediterranean vacation spots are even more reliant on U.K. tourists opening up their wallets: Malta and Cyprus, where this accounted for 25 and 23 percent of tourism spending, respectively. These two small nations came in second and fourth on S&P's 'Brexit Sensitivity Index,' which attempts to gauge susceptibility to possible after-shocks from a Leave vote.
As for where the fallout from a messy Brexit will be less acutely felt, look to the Danube River, or more precisely the four countries along its route—Austria, Bulgaria, Hungary and Slovakia—that rely on the U.K. for less than 3 percent of their trade and tourism.