By Paul Reynolds
World affairs correspondent, BBC News
The appointment of David Miliband as foreign secretary signals a potential shift in British foreign policy to one in which criticism of the United States and Israel is not off the agenda - as it was under Tony Blair.
David Miliband arrives at the FO
Within the Cabinet, Mr Miliband criticised the Israeli attack on Hezbollah last summer while his prime minister was defending Israel.
He made a speech in the United States as environment secretary last year in which he said that climate challenge would be met only with "strong leadership" in Washington.
His interest in climate change will mean that the innovation introduced by his predecessor, Margaret Beckett, to the Foreign Office - to make it an issue for diplomacy - will be continued and probably strengthened.
Another sign of change is the appointment as minister for Africa, Asia and the UN (with a right to attend cabinet meetings) of Mark, now Lord, Malloch Brown. As a key aide to the former UN Secretary General Kofi Annan, he was critical of the Bush administration.
His position, allied to that of a beefed-up department for International Development, shows Gordon Brown's interests in Africa and a new emphasis on Asia, which means China and India principally.
Mr Miliband, at 41 the youngest foreign secretary since David Owen was appointed in 1977 at the age of 38, is perhaps the epitome of a modern Briton.
Educated at a comprehensive school and at Oxford, he is from an immigrant family of Polish Jews.
His father Ralph changed his name from Adolphe when he arrived in England, and escaped from Belgium - to which his family had moved from Poland - by getting one of the last ships across the Channel in 1940.
Ralph Miliband became a leading Marxist writer, yet David emerged as one of the main thinkers behind the phenomenon known as "New Labour".
David Miliband's brother Ed is also a member of Gordon Brown's cabinet.
Deciding about Iraq
David Miliband's Jewish background will be noted particularly in the Middle East.
Many Israelis and Jews around the word will welcome the fact that someone with his dramatic family history has made it to one of the high offices in British and world diplomacy. However, they, and the Israeli government, will judge him by his words and deeds not by his origins.
The biggest issue facing him will be Iraq, with three British soldiers killed there on the day of his appointment.
He is reckoned to be in favour of getting British troops out as soon as possible, consistent with Gordon Brown's declared policy of withdrawing when conditions allow.
Diplomats are wondering whether, as foreign secretary, he will become a blogger - recording his thoughts in an online weblog - as he was in the Department for the Environment, Food and Rural Affairs.
David Miliband's arrival at the Foreign and Commonwealth Office follows a 13-month spell as environment secretary.
He had entered the Cabinet in May 2005 as minister of communities and local government, serving in the department of Deputy Prime Minister John Prescott.
This was just four years after his election as MP in a safe Labour seat in north-east England.
Somewhat controversially, Mr Miliband had been "parachuted in" from outside to fight the 2001 general election.
It followed a surprise, eleventh-hour decision by sitting MP David Clark not to contest the seat.
He has been tipped as a future leader of his party, but stood for neither the leader nor deputy leader posts now occupied by Mr Brown and Harriet Harman.
The new foreign secretary was working in Mr Blair's policy unit in the mid-1990s when Labour was still in opposition.
After his party's landslide victory in 1997, he became head of the 10 Downing Street policy unit and, as such, was a key figure in the prime minister's so-called "kitchen Cabinet".
Since then he has moved quickly through the government's ranks.
Within a year he became a middle-ranking minister, after being handed the school standards brief.
And in 2004 he was made Cabinet Office minister, before going into the Cabinet itself 12 months later.
Prior to working for Mr Blair, Mr Miliband spent time at the left-leaning Institute for Public Policy Research and as secretary of the Commission on Social Justice.
Educated at Haverstock Comprehensive, he went on to Oxford to study politics, philosophy and economics, where he got a first.
He also took an MSc in political science at the Massachusetts Institute of Technology in the United States.
He is listed as president of South Shields Football Club, but is nevertheless an Arsenal supporter.