Ukraine and Russia are set to go into their first direct talks in more than three years.
Ukraine's President Volodymyr Zelensky had challenged Russian President Vladimir Putin to meet him in person in Istanbul, but the Russian delegation named only a lower-level team.
Here's a breakdown of what is known and not about the talks so far:
Who is expected to attend?
Russian President Vladimir Putin proposed Russia-Ukraine talks in a late-night address hours after Kyiv and European countries urged Moscow to agree to a full and unconditional 30-day ceasefire starting Monday.
After Mr Putin's address, Mr Zelensky said he would be willing to meet Mr Putin in Turkey "personally".
Kremlin aide Vladimir Medinsky is heading the delegation.
Other attendees include deputy foreign minister Mikhail Galuzin, deputy defence minister Alexander Fomin, director of Russian military intelligence Igor Kostyukov, and Yelena Podobreyevskaya, the deputy head of the Kremlin's directorate for humanitarian policy.
Brazil and China, two of Russia's partners, welcomed the talks in a joint statement.
Why Turkey?
Turkish President Recep Tayyip Erdogan said a "historic turning point" had been reached in efforts to end the Russia-Ukraine war and his country was ready to host talks between the two warring parties.
NATO member Turkey has sought to maintain good relations with both of its Black Sea neighbours since the Russian invasion began and has twice hosted talks aimed at ending the war.
At the talks in Istanbul in March 2022, Moscow and Kyiv officials met and discussed an outline to end the war.
But the 2022 talks broke down following Russia's retreat from the Kyiv suburb of Bucha, where hundreds of civilians were found killed following a month-long occupation by Russian forces.
Contact between the warring sides has been limited since and mainly dedicated to humanitarian issues like prisoner-of-war exchanges and the repatriation of soldiers' remains.
Where do the two parties stand?
The fundamental differences between Kyiv and Moscow are far from being resolved.
Russia insists talks need to address what it says are the "root causes" of the conflict, including the "denazification" and demilitarisation of Ukraine, two vague terms Moscow has used to justify the invasion.
It has also repeated that Ukraine must cede its territory occupied by Russian troops.
Kyiv said it will not recognise its territories as Russian - though Mr Zelensky has acknowledged that Ukraine might have to use diplomatic means to get them back.
The two warring parties are struggling to agree even on a ceasefire.
Read more:
Ukraine, Russia to hold first direct talks since start of war
Ukraine peace talks: What are Kyiv and Moscow's positions?
Ukraine had agreed last month to the US proposal of an unconditional ceasefire, which Mr Zelensky said was a prerequisite for negotiations.
But Mr Putin, whose troops have the momentum in parts of the frontline, rejected the proposal.
What's next?
Mr Zelensky said in Kyiv that the West should impose massive sanctions if Mr Putin skips the meeting.
French President Emmanuel Macron and German Chancellor Friedrich Merz, two top EU leaders, warned Russia that there will be new sweeping sanctions if no substantial progress is reached in Turkey this week.
The EU yesterday, a day before the Turkey talks, approved a fresh package of sanctions on Russia, which is already subject to over 20,000 restrictive measures, clamping down on its "shadow" oil fleet.
In late March, Mr Trump threatened to impose tariffs on Russian oil, earnings from which are vital for the country's budget, which is strained by high military expenditures for the grinding three-year war.
Republican Senator Lindsay Graham was advocating a 500% tariff on imports from countries that continue buying Russian oil, gas, and uranium.
