The EU's new leadership took office on Sunday, one month later then planned, promising a more united Europe that would be ready to face major challenges, especially fighting climate change.
Germany's Ursula von der Leyen became president of the European Commission and marked the occasion in a short ceremony with her top EU counterparts, including EU Council President Charles Michel who also started on Sunday.
The team took the reins as the 28-member union is faced with a mountain of difficulties, including the Brexit divorce with Britain and rising tensions with superpowers China and the United States.
Von der Leyen said the officials gathered, who also included European Central Bank chief Christine Lagarde, must meet a great responsibility as guardians of the European Union treaties.
"It is a responsibility towards the European people and towards our founding father and mothers, but it is also a responsibility towards our children," she said.
"It is our responsibility to leave a union that is stronger than the one we inherited: ... a continent in peace with rights and liberties (and) a single market with unprecedented economic opportunities," she said.
Former IMF chief Lagarde, who took over the ECB last month, stressed that the union had only recently left the damaging debt crisis and must look to the future.
"It's a formidable challenge that awaits us, but my hope is that... we may leave this age of repairing (the EU) to one of renovation and hope," she said.
Von der Leyen, who replaced EU veteran Jean-Claude Juncker, will lead a 27-strong team of commissioners who also began work on Sunday with a clear ambition to make Europe a global powerhouse on green policy.
European Parliament President David Sassoli said the MEPs would hold an extraordinary session on December 11 -- the eve of an EU leaders summit -- to receive the commission's first climate proposals, dubbed the "Green New Deal".
Von der Leyen's first trip on Monday will be to the COP25 meeting in Madrid which the former defense minister said would be a "starting point" for her New Deal plans.
Her first voyage outside of the EU will be on Friday to Ethiopia where she will meet Prime Minister Abiy Ahmed, this year's Nobel Peace Prize winner, and African Union chief Moussa Faki.
-'Expect a lot'-
The Sunday ceremony was officially the 10th anniversary of the latest European treaty that simplified EU governance, which remains complicated and often criticised as too removed from the continent's 500 million citizens.
"Europeans expect a lot and they are right," said Michel, a former Belgian prime minister, whose job is to coordinate EU leaders' summits where major decisions are made.
Von der Leyen's mandate was due to start November 1 but was delayed after three of her initial nominees to the commission were rejected during the parliamentary confirmation process in an unprecedented snub.
She was finally approved by MEPs on Wednesday winning a comfortable majority though doubts still linger whether she has the support to push through her ambitions that also include tighter regulation of big tech and securing an EU budget.
Juncker's commission faced a myriad of unforeseen problems in its five year mandate, including the 2015 migrant crisis that exposed a bitter east-west split, with Hungary and Poland unwilling to open their doors to refugees.
Greece's near eviction from the eurozone that same year also dominated the agenda, which was followed closely by Britain's shock vote to exit the EU and the election of US President Donald Trump, who slapped trade tariffs on Europe in 2017.