World Bulletin / News Desk
Moon and Kim shook hands across the border at the Panmunjom Joint Security Area before the South's leader accepted an unexpected invitation to step over briefly to the North's side.
They then both made their way on to South Korean soil for talks that are set to proceed across two sessions before an evening dinner.
Seoul's presidential office has made clear that a successful summit would mean taking concrete steps towards North Korea's denuclearization.
While Kim has already announced a freeze on nuke and missile tests, the United States expects Pyongyang to go further if it wants to free itself from global sanctions.
"I will hold good discussions with President Moon with a frank, sincere and honest attitude and make a good outcome," the North Korean leader declared as the meeting, broadcast live, got underway.
For his part, Moon celebrated Panmunjom's shift from being a symbol of division to peace. The border has been heavily guarded since the 1950-53 Korean War ended in a ceasefire rather than a peace treaty.
Kim is in line to hold a further summit with U.S. President Donald Trump by June, although the details are yet to be confirmed.
As the summit began, the White House struck a note of optimism that the talks would be able to achieve progress on an elusive peace on the Korean peninsula.
"The United States appreciates the close coordination with our ally, the Republic of Korea, and looks forward to continuing robust discussions in preparation for the planned meeting between President Donald J. Trump and Kim Jong Un in the coming weeks ," spokeswoman Sarah Sanders said in a statement.