Kim Jong-un has become the first North Korean leader to set foot in South Korea by crossing the military line that has divided the peninsula since the end of the Korean War in 1953.
North Korea's leader Kim Jong Un (L) and South Korea's President Moon Jae-in shake hands at the Military Demarcation Line that divides their countries at Panmunjom. Photo: AFP / KOREAN BROADCASTING SYSTEM
Smiling and waving, South Korean President Moon Jae-in met Mr Kim at the border before talks begin.
At the summit venue, Mr Kim said that he hoped for frank discussions.
The historic meeting will focus on the North's recent indications it could be willing to give up its nuclear weapons.
In a moment rich with symbolism, Mr Kim and Mr Moon shook hands on both sides of the border in the demilitarised zone.
The South Korean president briefly stepped into the border into North Korea as well - an unexpected moment.
"I am happy to meet you," Mr Moon told Mr Kim, reports say.
The leaders were met by an honour guard in traditional costume on the South Korean side. The pair walked to the Peace House in Panmunjom, a military compound in the demilitarised zone (DMZ) between the two countries, to begin talks.
"A new history begins now - at the starting point of history and the era of peace," read the message Mr Kim wrote in a guestbook at the Peace House.
The White House said it was hopeful the talks would make progress toward peace and prosperity. The Korean summit is seen as a prelude to a proposed meeting between Mr Kim and US President Trump by early June, an unprecedented move as no sitting US president has met with North Korean leader.
The focus of talks
At the summit, the two leaders will address North Korea's controversial nuclear weapons programme.
Seoul has warned that reaching an agreement to rid Pyongyang of its nuclear weapons will be "difficult". North Korea's nuclear and missile technology has advanced significantly since the sides' leaders last met more than a decade ago.
The meeting - the third of its kind following summits in 2000 and 2007 - is the result of months of improving relations between the two Koreas.
But Mr Kim's recent re-engagement and apparent concessions and have divided analysts, with some questioning the sincerity of his intentions.
Mr Kim announced last week that he would suspend nuclear tests for the time being.
The move was welcomed by the US and South Korea as a positive step, although Chinese researchers have indicated that North Korea's nuclear test site may be unusable after a rock collapse following its last test in September.
As well as addressing Pyongyang's nuclear ambitions, the leaders of the two Koreas are expected to discuss a path to peace on the peninsula to formally end the 1950-53 Korean War, and a series of economic and social issues.
How the summit will unfold
Every detail of the summit has been precisely planned - from the timetable to the dinner menu.
Official talks between Mr Moon and Mr Kim began at 10:30 local time at the Peace House in Panmunjom. The pair will break after the first session and will have lunch separately - with the delegation from the North crossing back to their side of the border.
At an afternoon ceremony, Mr Moon and Mr Kim will plant a pine tree using soil and water from both countries, to symbolise "peace and prosperity".
Following the tree planting, they will walk together before starting the next round of talks. The summit will conclude with the leaders signing an agreement and delivering a joint statement before dinner. The banquet will be held on the South's side - and a carefully planned menu has already been announced.
Kim Jong-un will be served the Swiss potato dish rösti - a nod to his time studying in Switzerland - along with the North's signature dish of cold noodles, and a North Korean liquor.
After dinner, the delegations will watch a video called "Spring of One", before Mr Kim returns home.
Korean leaders Kim Jong-un and Moon Jae-in meet at the Korean border. Photo: Screenshot
Who will attend
Mr Kim will be accompanied by nine officials, including his sister, Kim Yo-jong, who led the North's delegation to the Winter Olympics in South Korea earlier this year. Kim Yong-nam, North Korea's nominal head of state, will also attend.
In a rare move - one not seen at previous inter-Korean summits - the delegation will also feature top military officials and diplomats.
South Korea will send seven officials along with President Moon, including the ministers for defence, foreign affairs and unification. The chairman of South Korea's joint chiefs of staff was a late addition to his entourage.
The summit is the culmination of months of improving relations between the two countries, a trend few would have predicted as tension rose in recent years.
The rapprochement began in January when Mr Kim suggested he was "open to dialogue" with South Korea. The following month the two countries marched under one flag at the opening ceremony of the Winter Olympics.
Mr Kim's new appetite for diplomacy led to a meeting with senior South Korean officials in March, the first time officials from Seoul had met the young leader since he came to power in 2011.
- BBC