By Giles Hewitt
The leaders of South Korea, China and Japan will hold their first summit in more than three years, setting aside historical animosities and territorial disputes to focus on shared security and trade concerns.
No substantive breakthroughs are expected, but Sunday's meeting in Seoul is a symbolic statement of intent by Northeast Asia's three largest economies who all stand to reap significant diplomatic and economic gains from closer cooperation.
The focus is very much on economic ties, with China especially keen to boost trade links as it seeks to inject some fresh momentum into its slowing economy.
Also high on the agenda is North Korea whose nuclear weapons ambitions pose a worry - and threat - to all three countries, including China, which is the North's main diplomatic protector and economic benefactor.
The triumph of realpolitik will be capped on Monday by a first ever one-on-one summit between South Korean President Park Geun-Hye and Japanese Prime Minister Shinzo Abe after an extended diplomatic freeze.
It was the souring of Japan's relations with its two neighbours that triggered a lengthy hiatus in the annual trilateral summit mechanism after the last meeting in 2012.
Sunday's gathering actually fell slightly below the full summit level, with China represented by Premier Li Keqiang, rather than President Xi Jinping.
Observers say Li's comparatively technocratic style made it easier to keep the focus on economic co-operation and away from the sensitive issues that have dogged relations for decades.
Relations between Seoul and Tokyo have never been easy - clouded by sensitive historical disputes related to Japan's 1910-45 colonial rule over the Korean peninsula, especially the issue of Korean "comfort women" forcibly recruited to work in Japanese wartime military brothels.
Park, who took office in early 2013, had until now repeatedly refused to meet Abe, saying Japan had yet to properly atone for its past actions.
China has similarly bitter memories of Japanese wartime aggressions and is also at odds with Tokyo over sovereignty of an island chain in the East China Sea.
Observers will be watching for any progress in efforts to seal a trilateral free-trade agreement that would provide a counterpoint to the new US-led Pacific trade pact of which China and South Korea are not members.