Najib Razak comes from a Malaysian political dynasty
The new Malaysian Prime Minister, Najib Razak, has been sworn in.
He takes over as leader at a time when the country and its coalition government, which has ruled since 1957, are facing big challenges.
The Malaysian economy is suffering, and last year the main ruling party - which Mr Najib now leads - lost its crucial two-thirds majority in parliament.
That defeat led to the decision of the previous Prime Minister, Abdullah Badawi, to resign.
Mr Najib is also facing claims of corruption and an opposition allegation linking him in some way with the murder of a Mongolian woman - all of which he has strenuously denied.
"I, Najib Razak, who has been chosen to hold the post of prime minister, swear that I will carry out the responsibilities which I have been entrusted with to the best of my ability," the 55-year-old said at a ceremony overseen by the king.
"I will be true to Malaysia and will defend and uphold the constitution," he said.
The main ruling party, the United Malays National Organisation (Umno), is bitterly divided and has been told by Mr Badawi that it must reform or lose power.
Mr Najib's challenge will be to galvanise the party and reignite its links to broader Malaysian society.
Recent Malaysian reports suggest he has already taken steps in this direction by visiting Malaysian Chinese newspapers and speaking of the need to unite Malaysia's many races and groups.
Malaysia also faces intense economic problems as its exports decline amid the world financial meltdown.
Last month he unveiled a stimulus package worth $16.2bn (£11bn).
Mr Najib's first test of his own popularity will be during three special elections - one for parliament and two for state assemblies - on 7 April.
Mr Najib comes from a respected political dynasty and is the son and nephew of two former prime ministers.