In many ways, Warsaw will be a sequel to Wales.
Two years ago, NATO was in emergency mode. Today it is planning for a long and tense conflict.
Two years ago, the Atlantic alliance went back to basics, refocusing on its core mission of defending its members. Today it is methodically putting the pieces in place to contain and deter an increasingly revanchist Russia.
The last time NATO heads of state gathered, in Newport, Wales, back in September 2014, the annexation of Crimea and the conflict in eastern Ukraine were only months old, and Russia's aggressive stance toward the West was just taking shape.
"Hybrid war" was still a fresh term that everybody was scrambling to understand.
If Wales 2014 was about an immediate response to a crisis, the alliance's summit this week in Warsaw will be about building the stable and sturdy security architecture for a long-term standoff with Moscow.
Decisions made in the Polish capital on July 8-9, alliance officials say, will resonate for decades to come.
"It will be a sign of the new times, when we will redefine Western security to deal more appropriately with the sea-change we have witnessed in this realm," Estonian President Toomas Hendrik Ilves said in a speech in May.
The summit is also unfolding in the shadow of "Brexit," in the emotionally charged environment following the United Kingdom's vote to leave the European Union.
So what should we expect in Warsaw?
The Eastern Front
Deterring Russia and reassuring the NATO's frontline states that border it will, of course, be the dominant theme at the summit.
"Transatlantic leaders must confront a jarring reality: the peace, security, and democratic stability of Europe can no longer be taken for granted," former U.S. Ambassador to NATO Nicholas Burns and former NATO commander James Jones wrote in a recent report for the Atlantic Council.
Two years ago in Wales, NATO decided to set up new military facilities in Estonia, Latvia, Lithuania, Poland, and Romania, and established a new rapid-response force that could assist endangered members within two days.
In Warsaw, the alliance is expected to further reinforce its eastern flank with four combat battalions of up to 1,000 soldiers each in Estonia, Latvia, Lithuania, and Poland.
The United States, the United Kingdom, Germany, and Canada have agreed to command one battalion each.
The U.S.-led battalion is likely to deploy to Poland, probably in or near the Suwalki Gap, a roughly 100-kilometer stretch of the Polish-Lithuanian border wedged between Belarus and Russia's Kaliningrad region.
Military planners fear that in the event of a conflict, Russia could capture the gap, effectively cutting off the Baltics from the rest of the alliance.
The German-led battalion is expected to deploy to Lithuania, the British-led one to Estonia, and the fourth to Latvia.
Washington has also agreed to station a heavy brigade of 3,500 U.S. troops that will work in both the Baltic region and in Bulgaria and Romania, where a key base is being expanded for U.S. use as a training center.
Additionally, NATO Secretary-General Jens Stoltenberg said in June that the alliance will consider an offer from Romania to host and command a multinational brigade of between 3,000 and 5,000 troops that would coordinate training and also play a deterrent role.
"These are not war-fighting formations," Mark Galeotti, a senior research fellow at the Czech Institute of International Relations, said on The Power Vertical Podcast.
"A thousand troops here or there, no matter how good they may be and no matter how well-equipped, are not going to turn the tide in the case of an apocalyptic war with Russia. They are political markers. They say: 'if you want to go into these countries you are not just going to be killing Estonians and Latvians, but Americans and Germans.' This is very significant."
But what if deterrence fails?
Due to the geography of Northern Europe, military analysts say the Baltic states are vulnerable to a determined Russian advance even with significant NATO troops on the ground.
A recent war game by the RAND Corporation concluded that NATO would need seven brigades, including three with heavy armor, "adequately supported by air power...and other enablers on the ground" in order "to prevent the rapid overrun of the Baltic states."
But even that would not be "sufficient to mount a sustained defense of the region or to achieve NATO's ultimate end state of restoring its members' territorial integrity."
And this, analysts say, is one of the reasons NATO is increasingly looking to two nonmembers, Finland and Sweden, as increasingly close partners and allies.
"Without Finnish and Swedish help, NATO will be hard-pressed to defend the Baltic states against a determined Russian attack," Edward Lucas, author of The New Cold War, wrote recently.
And with Finland and Sweden on NATO's side, the equation changes substantially.
Neither of the two historically neutral countries are ready to join the alliance yet, but support for that is on the rise in both, particularly in Sweden. Both also commissioned studies this year to explore the effects of membership.
Sweden and Finland are clearly moving closer to NATO, a trend that will likely be very visible in Warsaw.
In May, Sweden's parliament approved a host-nation support agreement with NATO, allowing the alliance to more easily operate on Swedish territory during training or in the event of a conflict or other crisis.
This summer, Swedish and Finnish foreign and defense ministers participated in meetings in Brussels with their 28 NATO counterparts, the first time such a format was used.
Alliance officials say the formula, known as "28 plus two," is likely to be continued in the future.
Russia's annexation of Crimea and its militarization of the peninsula is also forcing NATO to look south, with a renewed focus on the Black Sea, which Turkey's President Recep Tayyip Erdogan has said risks becoming a "Russian lake."
"By invading Ukraine and annexing Crimea, Russian President Vladimir Putin has transformed the security situation in the Black Sea," Stephen Blank, a senior fellow at the American Foreign Policy Council, wrote recently.
In an effort to push back, Romania plans to offer a proposal in Warsaw calling for a permanent multinational naval patrol in the Black Sea.
Speaking at a press conference in June, Stoltenberg said the issue will be "on the table" at the summit due to the "substantial Russian buildup in Crimea."
But creating a so-called NATO Black Sea fleet is proving controversial.
Bulgarian Prime Minister Boiko Borisov has made it clear that his country is opposed to, and would not participate in, such an initiative.
At a press conference in June, Borisov said such a move would "turn the Black Sea into a territory of war" and that he "wants to see cruising yachts, and tourists, rather than warships."
Bulgaria's opposition means the issue will probably be one of the most hotly debated issues in Warsaw.
NATO will also be turning its attention to cyberwarfare in Warsaw, alliance officials say, continuing a trend that began in Wales.
"At our previous summit, we made clear that cyberdefense is part of NATO’s core task of collective defense, and confirmed that international law applies in cyberspace," a senior NATO official said.
"At Warsaw, we will take another step ahead: recognizing cyberspace as an operational domain, in addition to air, sea, and land."
Classifying cyberspace as a domain, the official added, will enable NATO to better manage its resources and integrate cyberdefense into its exercises, training, and responses to crises.
A French television network, a German steelmaker, the Polish stock market, the White House, the U.S. House of Representatives, the U.S. State Department, and The New York Times are among those who have been on the receiving end of Russian cyberattacks in recent years.
Additionally, NATO is also expected to formally approve a "comprehensive assistance package" for Ukraine that was approved in June.
Enlargement, however, appears to be off the table for the foreseeable future, with the exception of Montenegro, which signed as "accession protocol" with NATO in May, will participate in the Warsaw summit as an observer, and is expected to join the alliance some time next year.
On the eve of the summit, U.S. Secretary of State John Kerry visited Georgia and Ukraine to reassure those two countries that the alliance's door remains open.
"The official NATO 'open doors policy' for alliance enlargement remains in place but it is difficult to see how potential candidates such as Georgia, Moldova, and Ukraine can move forward," John McColl, a former deputy NATO commander, wrote recently.