Q&A: can US and North Korean leaders meet at such short notice?
Donald Trump and Kim Jong-un meeting: what happens next?
The sudden announcement that US President Donald Trump and the North Korean leader Kim Jong-un will meet by the end of May raises questions about whether preparations for such a momentous step forward in the history of the Korean dispute can be finalised at such short notice.
North and South Korea and their respective allies fought each other to a ceasefire in the 1950-53 Korean War and Pyongyang has for decades defied heavy sanctions to pursue its nuclear weapons and ballistic missile programmes. But it has offered to put them on the negotiating table if what it calls threats against it are eliminated.
Where will the summit be held?
All that has been confirmed so far is that the meeting will take place by the end of May, but the venue for this remains to be decided.
If it happens in Pyongyang, Mr Kim is sure to put on a spectacular show for his visitor, but for America it would run the risk of appearing that Mr Trump is coming to pay his respects.
The Demilitarized Zone that divides the two Koreas - where Mr Kim and South Korean President Moon Jae-in are to meet in late April - is probably the most likely option at this stage, offering ease of access for both sides, a controlled environment, and facilities already in place.
It would also appeal to the two men's sense of drama.
A more neutral location with less weight of symbolism such as Beijing or Geneva - Mr Kim was educated in Switzerland -- would mean the three key players would have to plan events with another host nation.
Furthermore, it would involve a journey on both sides and Mr Kim has not left the North since inheriting power from his father in 2011.
Seoul would most likely be unthinkable to Pyongyang, and Washington even more so, but on the other hand no one would have predicted three months ago that Mr Kim's sister would visit the South Korean capital within weeks.
The United Nations headquarters in New York - Mr Trump's home town - would mean Mr Kim stepping on American soil, but it has a long history of hosting a rogues' gallery of world leaders.
Events have moved so far, so quickly and in such unforeseen ways that no option can immediately be ruled out.
How will Mr Trump prepare?
There also questions about Washington's preparedness for the meeting. Just hours before it was announced Secretary of State Rex Tillerson had said the US was "a long way from negotiations" with the North.
The North's diplomats are renowned as tough, wily negotiators - "very Machiavellian" in the words of one analyst, but under Mr Trump the State Department has lost many Korea specialists. The president he has yet to name an ambassador to Seoul - front-runner expert Victor Cha was reportedly ruled out of consideration because of his refusal to entertain the idea of a pre-emptive US strike on the North.
The US Special Representative for North Korean policy Joseph Yun retired last week, and there has been none of the diplomatic groundwork that usually precedes a meeting between heads of state.
"Summits normally come at the end of a long series of negotiations at lower levels in which lots of devils in the details are hammered out," said Pusan National University associate professor Robert Kelly.
"Trump, always the publicity-seeker, is just diving right in," he tweeted, warning there was a risk he "will wander from decades of joint US-South Korea policy, about which he naturally knows nothing, and make some kind of deal for a 'win' that no other US official would endorse".
How are the two men likely to get along?
Mr Trump and Mr Kim are radically different but in other ways strikingly similar. Mr Kim was chosen to inherit power and was groomed to do so for years, while Mr Trump is one of the unlikeliest US presidents in history, reaching the White House via a career in property development and reality television.
Mr Kim has far more experience in office - more than six years - and expects to rule for decades, planning for the long term accordingly with no concern about the next day's headlines in his state-controlled media.
But both men prize personal loyalty, counting family members among their closest advisers, and they share a taste for theatre - Mr Trump has called for a military parade in Washington, something Mr Kim holds in Pyongyang usually every year.
They traded threats and personal insults last year, with Mr Trump dubbing Mr Kim "little Rocket Man" while menacing the North with "fire and fury" that would "completely destroy" the country.
In turn Mr Kim called him a "mentally deranged US dotard".
But Mr Trump is known for his sudden turnarounds and tweeted in November: "I try so hard to be his friend - and maybe someday that will happen!"
What is South Korea's role?
Strikingly, all the key announcements of recent days have been made by South Korea.
Its envoys revealed both North Korea's willingness to negotiate over its nuclear weapons and - on the White House lawn, with no US officials present - Mr Trump's acceptance of the offer to meet.
In the early months of Mr Trump's presidency he focused on China as a way to influence the North and developed a friendship with Japan's Shinzo Abe, leading to fears in Seoul that the South was being bypassed - reinforced when he accused President Moon Jae-in of "appeasement".
But Mr Moon has seized the opportunity presented by the Winter Olympics to try to broker talks between the rivals - while repeatedly crediting Mr Trump's assertive approach for Mr Kim's willingness to talk.
How will China react?
The outcome of the Trump-Kim meeting will have great significance for China, which for decades has been North Korea's key diplomatic protector and main source of trade and aid, although the relationship has soured in recent years.
Mr Kim has not travelled to Beijing to pay his respects to President Xi Jinping, and Beijing has become increasingly frustrated with its neighbour's behaviour, showing a new willingness to agree to tougher sanctions against it - and enforce them.
At the same time it fears the collapse of the regime in Pyongyang and the instability it would bring, potentially sending waves of refugees into China and the possibility of US troops stationed on its border in a unified Korea.
However, any agreement that could lead to a reduced US troop presence in the South would also by implication tilt the balance of power in Beijing's favour in a region it increasingly sees as its own back yard.