Outspoken Anglican leader Dr Rowan Williams has been enthroned as the 104th Archbishop of Canterbury.
Dr Williams, who has made clear his opposition to war with Iraq, said his enthronement marked the moment when his job truly began.
He was installed at a ceremony at Canterbury Cathedral, attended by figures including Tony Blair, Prince Charles, Tory leader Iain Duncan Smith and representatives of other churches and faiths.
Dr Williams entered the cathedral just after 1500 GMT, knocking on the massive wooden doors with his staff.
Music, hymns, prayers and blessings followed until his enthronement about 1535 GMT.
Traditionalists protest
The new archbishop has courted further controversy with his support for gay rights in the church and the ordination of women priests.
Church traditionalists threatened to protest outside the cathedral wearing black armbands in anger at his views on homosexuality.
But the activists most in evidence were those protesting against the war against Iraq.
The ceremony itself had many non-traditional elements to reflect the global constituency of the church.
Unusual touches included musical interludes from a Welsh soprano accompanied by a harp and from a group of African-influenced singers and drummers.
And true to his reputation as a maverick, the new archbishop opted for an unusual start to what proved to be a slightly unorthodox sermon.
There was a polite chuckle when he started: "It's sometimes been said that if someone came up to you in the street and whispered: 'They've found out! Run!', nine out of 10 of us would."
War protest
He concentrated on the value of tolerance of differences and cautioned against using any single group in society as a "scapegoat".
But the cleric also urged Christians to engage the world of politics.
"When Christians grieve or protest about war, about debt and poverty, about prejudice, about the humiliations of unemployment... it is because of the fear we rightly feel."
Dr Williams was installed in the 13th Century marble chair of St Augustine after swearing an oath on the 1500-year-old Canterbury gospels.
Representatives from the major faiths in Britain including Jews, Muslims, Hindus, Sikhs and Buddhists all attended the service.
Although the ceremony was a moment of celebration for the world's 70 million Anglicans, some evangelicals reject Dr Williams' liberal social views - especially those on homosexuality.
Others hope that he will modernise the church and reverse its loss of membership.
Dr Williams has said his future role will involve far more than formulating Christian opinion on current issues.
The way he has repeatedly challenged politicians suggests he will try to lead a more active national moral debate.
Consumer pressure
Dr Williams has called for wealth to be redistributed and has also criticised Anglicans for being too keen on status and titles.
He used a high-profile lecture last month to claim that politicians often developed policies in response to consumer pressure - at the expense of moral leadership.
On the subject of refugees he said that asylum seekers could be held in secure accommodation, until it was clear that they posed no danger.
Dr Williams legally became the Archbishop of Canterbury at the Confirmation of Election ceremony in St Paul's Cathedral in December.