Members of NATO met on Tuesday for the start of a two-day summit to discuss a variety of security issues — including the war in Ukraine. This will be the fourth time the defense alliance has met since Russia invaded Ukraine in February 2022. The summit is taking place in Lithuania’s capital Vilnius, one of NATO’s most eastern flanks.

But what’s on the agenda this week? Below are four main issues to watch for.

Ukraine's membership

NATO Secretary-General Jens Stoltenberg reaffirmed that Ukraine would become a member of NATO and announced the alliance had agreed on a procedure with one step instead of the usual two — speeding up the process. A multi-year assistance program will also be brought in for Ukraine to help bring it up to NATO standards. This will “enable the transition from Soviet-era to NATO standard training and doctrines,” Stoltenberg said.

In April, Stoltenberg announced that all 31 members had agreed that Ukraine would join the alliance when the war ended. "President [Volodymyr] Zelensky has a very clear expectation; we discussed this," Stoltenberg told reporters at the time. Over the two-day conference, NATO will decide how to proceed with Ukraine's membership.

“That's clearly the most delicate issue of the summit,” Jamie Shea, former deputy assistant secretary-general for emerging security challenges at NATO, told Yahoo News. “It's also the one that has gone down to the wire that hasn't been fixed in advance by NATO ambassadors back in Brussels.”

At the annual summit in 2008, NATO declared that Ukraine would join the alliance. As time went on, though, it seemed as though Ukraine had been left on the sidelines. Six years later, Russia would take Crimea. If Ukraine had been part of NATO at that time, Russia would have been engaging in war with all the other 31 members.

On Sunday, President Biden reiterated that the current war would have to end before any consideration could be made about Ukraine's NATO membership. If Ukraine were to join NATO, then all member states would be at war with Russia. "We're determined to commit [to] every inch of territory that is NATO territory," Biden explained. "If the war is going on, then we're all in war."

Despite not being a member, Zelensky was invited to attend the summit on its final day. “So, clearly he has high expectations of the kind of message that he's going to get from the allies regarding Ukraine's future membership,” Shea added.

Zelensky said on Tuesday that it would be "absurd" if NATO did not set a timeframe for Ukraine's future membership. "For Russia, this means motivation to continue its terror," he added.

As NATO members have been supplying Ukraine with weaponry since the invasion began, another matter of discussion will be the plan going forward to help Ukraine’s success in the war.

Sweden’s accession

On the eve of Tuesday's summit, Turkish President Recep Tayyip Erdogan agreed to support Sweden's membership to the military coalition following months of ongoing negotiations. Turkey will ask its parliament to advance Sweden's membership "as soon as possible," Stoltenberg said on Monday, adding, "Completing Sweden's accession to NATO is a historic step that benefits the security of all NATO allies at this critical time." When exactly this would happen was not immediately clear.

"Erdogan didn't want to be isolated [at the summit] and now he is occupying center stage," Shea said regarding Erdogan’s sudden change of mind.

For months, Sweden's NATO bid had been repeatedly thwarted by both Turkey and Hungary. Then on Monday, Erdogan said that Turkey would remove its veto if the European Union considered Turkey as a future member.

On Tuesday, Hungary echoed Turkey's decision to greenlight Sweden's accession to NATO, Euronews reported. "Our position is clear: the government supports Stockholm's accession to the Atlantic Alliance," Hungarian Foreign Minister Peter Szijjarto wrote on Facebook. "Completing the ratification process is now just a technical matter."

Collective defense

Another priority at the summit this week will be to discuss NATO's collective security and individual members' ability to defend themselves. This includes arranging different types of training and purchasing new weapons. Since Russia's invasion of Ukraine, NATO has been steadily improving its defense against different scenarios — including attacks by the Kremlin and its allies. "These attacks can't be ruled out any longer," Shea said.

Asia-Pacific partners

Unlike previous NATO summits, four leaders from the Asia-Pacific region — Australia, New Zealand, Japan and South Korea — have been invited to the talks. It is believed the discussions will be about similar security issues faced by all nations.

“NATO is concluding quite ambitious individual partnership agreements with these four countries to do things like maritime security, climate change, cyber defense, critical infrastructure, protection and technology,” Shea said. “I think there'll be a bit of interest about how NATO sees China, as well as Russia, and how it sees the future development of its relations and its role with the Indo-Pacific countries.”