The ceasefire agreement brokered by Russia and Turkey and approved by the Syrian government and some of its most powerful rebel opponents is a potential turning point in the Syrian civil war.
The conflict has killed hundreds of thousands of people and laid waste to huge parts of the country over the past six years.
Today's announcement comes days after government forces recaptured the northern city of Aleppo, scoring its most symbolic and strategic victory in the conflict.
If it sticks, the ceasefire will lead to the convening of talks between the Syrian government and the opposition to be held in mid-January in the former Soviet republic of Kazakhstan, the first such talks since UN-sponsored peace talks collapsed in April this year.
Here is a look at the ceasefire agreement:
WHO ARE THE MAIN PLAYERS?
Russia and Turkey are the main sponsors of the agreement and say they will be the guarantors of the truce. The two countries support opposing sides of the civil war and earlier this month negotiated a ceasefire in rebel-held Aleppo that allowed opposition fighters and civilians to evacuate. The Syrian government has confirmed the ceasefire, and its main regional ally, Iran, welcomed the agreement. Russian foreign minister Sergey Lavrov said other key nations with influence in Syria, including Saudi Arabia, Qatar and Jordan, may join at a later stage.
Conspicuously missing from the equation is the United States. US secretary of state John Kerry has been heavily invested along with Mr Lavrov in past efforts to bring about a ceasefire, but all previous attempts have been unsuccessful. The US has in recent months all but handed over the Syria file to Russia, and it is unclear what incoming President Donald Trump will bring to the table. He has, however, suggested he would be more focused on the fight against Islamic State (IS) than the removal of Syrian president Bashar Assad from power.
WHICH OPPOSITION GROUPS ARE INCLUDED?
Most of the major mainstream rebel groups have signed on to the ceasefire agreement.
Osama Abo Zayd, a Turkey-based legal adviser for an umbrella group of rebel factions known as the Free Syrian Army, said 13 rebel groups have signed the agreement and that more are on board but were unable to make the signing in Ankara because of bad weather. He did not list them.
The Russian defence ministry listed seven groups, including the powerful, ultraconservative Ahrar al-Sham, the Army of Islam, which is particularly active around the Syrian capital, and the Army of Conquest, which is led by the al Qaida affiliate and controls the northern province of Idlib.
Russian defence minister Sergei Shoigu said opposition units totalling 62,000 fighters have agreed to adhere to the truce, saying they "control most of the territory in central and northern Syria outside Damascus's control".
WHICH GROUPS ARE NOT INCLUDED?
According to Russia and the Syrian government, IS and the al Qaida affiliate in Syria, the Fatah al-Sham group, are excluded. That is in line with previous ceasefire agreements, which eventually crumbled largely because of the blurred lines between the al Qaida-linked group and other rebel factions that co-operate with it.
Mr Abu Zayd, speaking at a press conference in Ankara, said the main Kurdish militia in Syria, known as the YPG, was also excluded. The US-backed group has been the most effective force in fighting IS in northern and eastern Syria, but is considered by Ankara to be a terrorist organisation.
IS THIS A BREAKTHROUGH?
The deal is a potential turning point in the six-year civil war. The balance of power has shifted greatly in Assad's favour over the past year, capped by the recapture of Aleppo, Syria's largest city and former industrial capital, a few days ago. The loss of Aleppo has been a humiliating defeat for the opposition, which has been largely abandoned by its allies in the fight for its most important stronghold. The US administration has been noticeably absent from negotiations in Moscow that involved Russia, Iran and Turkey last week. The warming of ties between Moscow and Ankara and their joint work on Syria now offers the best chance for a political settlement to the war.
WHAT ARE THE MAIN POINTS OF AGREEMENT?
Mr Abu Zayd said the agreement is made up of five points, including political negotiations to be held within a month of the ceasefire. He said the sides agreed to work together to forge a settlement for the Syrian conflict based on the Geneva communique and UN Security Council resolution 2254, which envisions an 18-month timetable for a political transition in Syria, including the drafting of a new constitution and elections.
Both documents, however, do not clearly address Assad's role in any political transition and chances for a breakthrough remain slim as distrust and continuing disagreements between rival factions still run deep.
CAN VIOLENCE DERAIL THE DEAL?
Yes. There are dozens of rebel factions in Syria including extremist groups that have not signed up for the deal. Maintaining the ceasefire will also be highly challenging because it excludes powerful groups such as IS and the Fatah al-Sham group.
Assad has repeatedly said in recent weeks that he is intent on retaking every inch of Syria, suggesting he still believes in the military option and may not be enthusiastic about holding up his end of the deal.
Russian president Vladimir Putin described the agreements reached as "quite fragile", requiring "special attention and patience".