By Jonathan Head
BBC News, Bangkok
Abhisit Vejjajiva has a reputation for 'clean politics'
He is the youngest prime minister Thailand has had for more than 60 years, and perhaps the most articulate and telegenic.
He is untainted by corruption or conflicts of interest, which is almost unheard of in Thai politics, especially for someone who has been in parliament for 16 years.
Abhisit Vejjajiva's strengths are well known in Thailand. He will need them all, and a lot more. It is hard to imagine a prime minister starting a term of office in less favourable conditions.
His first and most difficult challenge is calming the intense political atmosphere that has seen the country bitterly divided between supporters and opponents of the exiled former Prime Minister Thaksin Shinawatra.
It is all the harder for Mr Abhisit, as his party has allowed itself to become closely associated with the hard-core People's Alliance for Democracy (PAD), whose campaign of economic sabotage, culminating in last month's week-long occupation of Bangkok International Airport, helped bring down the previous government.
The furious reaction of the ousted government's supporters outside parliament, when they hurled metal barriers at the gates and smashed cars belonging to Democrat MPs, may foreshadow further violent opposition to the new administration in the pro-Thaksin heartland of the north and north-east.
People there accuse the Democrats of conspiring in a "silent coup", together with the PAD, the military and elements of the royalist elite, to bring down an elected government.
Born in Britain, educated at Eton and Oxford
Entered parliament in 1992 as one of its youngest members
Party leader since 2005
Opposed military coup that overthrew Thaksin Shinawatra
It does not help that the British-educated Mr Abhisit is often perceived here to lack a common touch, making it difficult for him to reach out to angry Thaksin supporters who are mainly from poorer rural regions. He barely campaigned there during last year's election.
For its part, the PAD says it will resume its protest campaign if there is insufficient progress towards its concept of "new politics", which includes a partly appointed parliament, something the Democrats oppose.
Mr Abhisit's second challenge will be to rebuild confidence in an economy that is headed for trouble.
The full cost of the airport occupation has yet to be fully counted, but it will certainly run into several billions of dollars. The long-term damage to investor and tourist confidence could be much worse - and that comes on top of a rapidly deteriorating global climate.
Thailand's National Economic and Social Development Board now concedes that its prediction of 3-4% economic growth next year is far too high.
Some economists here are predicting that the economy will shrink, a dire prognosis for this high-performance region. More than a million Thai jobs are expected to be lost next year.
The Democrats have strong candidates in mind for the key economic portfolios - Mr Abhisit himself has an MA in Economics from Oxford.
But to stitch their winning coalition together, they have had to trade away many other cabinet positions to the smaller parties and factions that defected from the previous government.
Passions are still inflamed on all sides
These are expected to keep the same ministerial portfolios they had before, despite the dismal performance of their candidates in those posts so far this year.
Then there are the questions over how much authority Mr Abhisit will really wield over his government, and even his party.
His may be the fresh new face, but behind him the wheeling and dealing for the Democrats is done by veteran party godfathers, in particular Secretary General Suthep Thaugsuban, a politician whose public image is far removed from the squeaky clean Mr Abhisit.
It was Mr Suthep who did all the hard bargaining to win over defecting factions from the Thaksin camp.
The potential instability of Mr Abhisit's coalition will also make it hard for him to drive through effective policies, at a time when the country is crying out for them.
His margin of victory in parliament was 37 votes, out of a total of 436; that could shrink after by-elections in January for the 29 MPs banned in November's court ruling against the former government.
It is narrow enough for his coalition partners to be able to exert a lot of influence, should they disagree with Mr Abhisit's policies.
So expectations of this new government are low. Just lasting more than a year would be an achievement.
But if Mr Abhisit can bring about a return to something like normal government, and an end to turmoil on the streets, he may yet earn the gratitude of a politically exhausted population.