The most volatile issues and the key personalities involved in the July 7-8 G-20 meeting in Hamburg:
North Korea's first successful test of an intercontinental ballistic missile (ICBM) on Tuesday is likely to overshadow all other trade and diplomatic rows.
The reclusive state's relentless pursuit of its nuclear ambitions comes as a slap in the face for US President Donald Trump, who vowed that Pyongyang's goal of possessing an ICBM "won't happen".
Germany has made climate protection a priority of its G-20 presidency. It had hoped to get the world's biggest industrialised and emerging economies to commit to taking the lead in implementing the landmark 2015 Paris climate deal.
But Mr Trump dashed those hopes after vowing last month that he would pull the world's second-biggest carbon emitter out of the Paris accord.
LOOMING TRADE WAR
Signing up to an anti-protectionist pledge used to be routine at G-20 meetings, but not this time.
Mr Trump, swept to power by popular anger over de-industrialisation in vast parts of the United States, has pledged to "follow two simple rules: buy American and hire American". That has put him at odds with many US trading partners, including export giants Germany and China, which he has criticised over their massive trade surpluses.
Mr Trump's threats may soon materialise, as Washington is reportedly preparing to impose punitive tariffs on steel imports - something that G-20 exporters would be keen to ward off.
With accusations of Russian meddling in the US elections and contacts between Mr Trump's senior aides and President Vladimir Putin's men, the vexed relationship between the two will be closely scrutinised when they meet face to face for the first time tomorrow.
The two leaders face various issues of contention, from Syria to Ukraine to North Korea.
Mr Trump has struck a tough tone on Russia's ally Syria, while Washington's decision to toughen sanctions over the conflict in Ukraine has angered Moscow.
Another meeting to watch will be Mr Trump's talks with Chinese President Xi Jinping, particularly after the US billionaire leader in a tweet accused Beijing of not doing enough to rein in North Korea.
Mr Trump infuriated Beijing last week when he approved a US$1.3 billion (S$1.8 billion) arms sale to Taiwan, while China lashed out after a US warship sailed close to an island claimed by China, Taiwan and Vietnam.
German Chancellor Angela Merkel also faces a testy meeting with Turkish President Recep Tayyip Erdogan, particularly after Berlin refused him permission to address ethnic Turks on the sidelines of a summit. Berlin and Ankara's relations have been fraught, deteriorating sharply over Turkey's mass crackdown after a failed coup last year and a host of other rights controversies.