At 12:30 p.m. on Wednesday afternoon, Sir Tim Barrow, the U.K.’s permanent representative to the EU, will hand-deliver a letter from British Prime Minister Theresa May to the office of European Council President Donald Tusk in Brussels, officially notifying the European Union of the U.K.’s intention to leave the 60-year-old bloc. The delivery of that letter will trigger Article 50, the statute of the EU Lisbon Treaty governing the procedure for the withdrawal of a member state.

The highly anticipated—and, for many, much-dreaded—“Brexit day” has been the subject of endless agonizing and political maneuvering since long before last Monday, when May announced the specific date upon which she will begin the years-long process of removing the U.K. from the EU. Yet many analysts say Wednesday’s invocation of Article 50, the first time a member state has ever signaled its intention to leave the EU, will be uneventful.

“On the one hand it's a really big step—it means that Britain is formally starting the clock [on negotiations], but at the same time, it’s a bit of a phony war until the autumn,” said Mark Leonard, director of the European Council on Foreign Relations, pointing to April’s presidential elections in France, and the German federal election in September, as factors in the protracted divorce proceedings between the EU and U.K.  

And to potentially further delay matters, after Wednesday, the U.K. will remain part of the EU for at least two years, the time Article 50 allows for negotiations over Britain’s exit. According to the text of the statute, however, that interval can be extended if the European Council and the U.K. agree to do so.

But others warn that March 29 could invite a reprisal of “Black Wednesday,” the infamous 1992 collapse that occurred on the day Britain withdrew from the European Exchange Rate Mechanism, causing the pound to collapse by 15 percent. Earlier this year, uncertainty over the U.K.’s departure from the EU caused the pound to tumble after May outlined her commitment to a “hard Brexit” that would extract the country from the European single market. When May reiterates that promise on Wednesday, some fear the pound could suffer another hit. But her decision to announce Brexit day a week in advance has allowed the markets to take it into account, likely avoiding any immediate damage to the pound, according to Richard Whitman, senior research fellow at Chatham House.

So despite the unprecedented nature of Wednesday’s events, British society—the government, financial markets, and average citizens, at least—seem to be approaching the portentous day in a decidedly British way: calmly. Yet even as Brits plan to carry on as usual, there is hardly anything normal about what is about to happen.

Brexit negotiations will come in two phases: the first, which begins on Wednesday, is a battle over what the divorce settlement between the U.K. and EU will look like. The two most important issues in those proceedings concern how much the U.K. will have to pay the EU upon leaving—current estimates are around $60 billion, though Brexit Secretary David Davis swore on Monday the sum would be “nothing like that.” The other issue is securing the rights of EU citizens living in the U.K., and U.K. citizens living in Europe. May has said she would like to reach an early agreement to secure the reciprocal rights of EU and U.K. citizens; arriving at such an agreement in the first few months of negotiations could be an easy win for both sides. In the meantime, the rights of EU citizens in the U.K. will indeed be used as “bargaining chips” in Brexit negotiations. Many families have already begun preparing to leave the country, fearing their loved ones may be denied the right to live or work in a post-Brexit Britain.

“There will be a degree of … treading water for the next six months,” Leonard said. “The big crunch point will be in December [2017] when there will be an agreement about the divorce.” Once leaders on both sides reach an amicable divorce settlement, they will begin tracing the contours of their future relationship—in particular, the future of trade between them.

On Monday, the Labor Party and UKIP both issued six “tests” for Brexit, providing a general notion of how both opposition parties will evaluate the eventual exit deal. On Thursday, the U.K. will publish a white paper detailing its intention to introduce the Great Repeal Bill, a measure that would transfer all EU laws into U.K. law while repealing the European Communities Act 1972, which marked the U.K.’s accession to the EU 45 years ago. Parliament would then have to vote to remove or modify EU laws that currently apply to the U.K., potentially returning some powers to the devolved parliaments and assemblies of Scotland, Northern Ireland, and Wales. Then, on Friday, the EU will respond to May’s letter with draft negotiation guidelines for the remaining 27 member states, outlining the bloc’s priorities for the ensuing two years of negotiations. A month later on April 29, representatives from all 27 states will meet for a special Brexit summit to discuss their negotiating position.

Three elements of uncertainty hang over May’s upcoming announcement. The first is what, exactly, her letter will say. The prime minister is expected to outline the U.K.’s position entering Brexit negotiations, and perhaps elaborate on what kind of relationship she hopes the U.K. and EU will have post-Brexit. But she is unlikely to elaborate on the government’s previously held positions on questions like the rights of EU citizens living in the U.K., a U.K.-EU trade agreement, foreign policy, and environmental commitments. “The thing that will be interesting to watch out for will be whether [the letter] says anything more about the position of EU nationals living in the U.K., whether it says anything about the divorce bill—any payments the U.K. has to make to the EU on leaving. My guess is it probably won’t,” Jonathan Portes, professor of economics and public policy at King’s College London, told me.

The second unknown is how the EU will respond to the U.K.’s notification. The European Parliament and a “super qualified majority” of the European Council—or 72 percent of member states—will have to agree upon the eventual Brexit deal, according to a European Parliament brief on the withdrawal process. Additionally, all 27 European national parliaments will have to vote on a post-Brexit EU trade deal with the U.K. and any other European treaty changes. Fractures in the bloc, particularly among the Visegrad Group nations—Poland, Hungary, Czechia, and Slovakia—have already complicated debates over migration and the creation of a “multi-speed Europe,” and could create further road blocks. As member states prepare to meet in April, a sharper portrait of their varied priorities in talks with the U.K. will emerge. “Nothing will be settled in April, but we will get an idea of whether these are going be … really nasty, conflicting negotiations, or whether both sides want to come to a quick agreement,” Portes said.

The third question is whether Article 50 is setting the U.K. on an irrevocable path toward leaving the EU, or whether it is reversible. The author of the five-point statute, Lord Kerr of Kinlochard, argued last month that triggering Article 50 does not necessarily mean the country must commit to following through with Brexit. “If, having looked into the abyss, we were to change our minds about withdrawal, we certainly could and no one in Brussels could stop us,” he told the House of Lords. The government has “decided to put our autarchic sovereignty ahead of economic well-being. It is a sad fact that it will not be those who got us into this fix who will suffer. The Bullingdon boys will be just fine; the country may not,” he said, referencing the notorious Oxford drinking club whose alumni include former prime minister David Cameron and his chancellor of the exchequer George Osborne, as well as current Foreign Secretary Boris Johnson.

While Article 50 may be legally reversible, the political repercussions of such an about-face would be severe for May’s Conservative Party. “It is difficult to imagine the current government making a u-turn without creating a civil war within the Conservative Party,” Chatham House’s Whitman said.

It’s not certain what would happen if the two-year negotiations fail to produce a deal, or produce one that the U.K. refuses to accept. “It is clear from our evidence that a complete breakdown in negotiations represents a very destructive outcome, leading to mutually assured damage to the EU and the U.K. Both sides would suffer economic losses and harm to their international reputations,” Conservative MP Crispin Blunt said earlier this month.

“There’s a 30 to 40 percent chance it becomes impossible to do a deal,” Leonard said. “If negotiations fail without an agreement to extend the deadline, then Britain simply falls out of the EU and has the same rights as any other country in the World Trade Organization—that's the nuclear action. The British threat is that if that happens it won’t pay up the [$62] billion [divorce bill], so both sides would lose.”

Yet if all somehow goes according to plan, negotiations will be completed by October 2018, giving the Houses of Parliament and European Council and Parliament four months to vote on the resulting deal. The earliest the U.K. could formally leave the EU would be March 2019. For officials on both sides of the English Channel, it will be a long two years. “This is not the beginning of the end, but it might the end of the beginning,” Portes said.