The United States and Russia hailed a breakthrough deal on Saturday to put Syria's peace process back on track, including a nationwide ceasefire.
The deal, agreed upon by US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov, aims at halting fighting in Syria and moving toward a political transition after over five years of combat between President Bashar al-Assad's forces and opposition rebels.
Here is a closer look at the deal.
What the agreement says
A nationwide ceasefire by Assad's forces and the US-backed opposition is set to begin across Syria at sundown on Monday.
That sets off a seven-day period that will allow for humanitarian aid and civilian traffic into Aleppo, Syria's largest city, which has faced a recent onslaught.
Fighting forces are to also pull back from the Castello Road, a key thoroughfare and access route into Aleppo, and create a "demilitarised zone" around it.
Also on Monday, the US and Russia will begin preparations for the creation of a Joint Implementation Centre that will involve information sharing needed to define areas controlled by the Jabhat Fateh al-Sham group (formerly known as al-Nusra Front) and opposition groups in areas "of active hostilities".
The centre is expected to be established a week later, and is to launch a broader effort toward delineating other territories in control of various groups.
As part of the arrangement, Russia is expected to keep Syrian air force planes from bombing areas controlled by the opposition. The US has committed to help weaken Jabhat Fateh al-Sham, an al-Qaeda affiliate in Syria that has intermingled with the US-backed opposition in several places.
A resumption of political dialogue between the government and opposition under UN mediation, which was halted amid an upsurge in fighting in April, will be sought over the longer term.
Who is on board
Kerry said the US-supported opposition and other fighters will be called upon to set themselves apart from the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) and the Jabhat Fateh al-Sham.
Lavrov said through a translator: "The Syrian government has been informed of these arrangements and is ready to fulfill them."
How the arrangement came together
The Geneva negotiating session lasted more than 13 hours and capped a flurry of meetings between the two diplomats in recent days.
Kerry and Lavrov met four times since a previous Geneva meeting on August 26, and Presidents Barack Obama and Vladimir Putin discussed the matter at a summit in China.
What makes the agreement different
The US and Russia, ultimately, are to find themselves fighting together against ISIL and Nusra, and embarking on unprecedented information-sharing, aimed at dispelling longstanding mistrust between the two powers over the Syria conflict.
Kerry acknowledged "confusion" over Jabhat Fateh al-Sham and "legitimate opposition groups" that had led to a "fraying" of a ceasefire that was shepherded earlier this year by the US and Russia and brought a badly-needed, if temporary, respite to Syrian civilians for several weeks.
Will the agreement work
For the agreement to work, Russia will need to persuade the Syrian air force to stop strikes on anti-government positions, which have killed large numbers of civilians.
In turn, Washington has to get the opposition groups it backs to separate themselves from Jabhat Fateh al-Sham, which has allied itself with a range of rebels at different points in the fluid conflict.
"The armed opposition in Syria now faces what is perhaps its biggest and most momentous decision since they chose to take up arms against the Assad regime in 2011," said Charles Lister, a senior fellow at the Middle East Institute think-tank.
Mainstream rebels appear reluctant to withdraw from frontlines where Jabhet Fateh al-Sham fighters are also present because of fears the ceasefire will fail, he said.
"For this reason alone, many opposition figures see the US-Russia talks and whatever comes from them as a conspiracy against their long and hard fought for revolution. It will be hard to change this mindset," Lister added.
A truce agreed in February and endorsed by the United Nations Security Council has been repeatedly broken by both sides.