US President Donald Trump is in the UK for his historic second state visit, which will involve a crowded mix of royal pageantry, trade talks and international politics.
He will meet King Charles at Windsor Castle on Wednesday, having touched down late on Tuesday and spent the night at the US ambassador's London residence.
The president sent positive signals ahead of his journey to the UK aboard Air Force One, calling the visit an "honour" and describing his "very good" relationship with the UK.
A multi-billion US technology investment deal was announced as the visit got under way - but Trump said the trip's main purpose was to see "my friend" King Charles.
"He represents the country so well, such an elegant gentleman," he said.
Trump and First Lady Melania received an official welcome on the runway at Stansted airport by a line-up which included Foreign Secretary Yvette Cooper.
Prime Minister Sir Keir Starmer also held a short phone call with Trump late on Tuesday, to welcome him to the country.
He spent the night in Winfield House ahead of a day of royal ceremony and lavish spectacle in Windsor Castle - which he described as "the ultimate" setting.
Hosting him will be King Charles and a full line-up of senior royals, currently including Queen Camilla, who had to miss the Duchess of Kent's funeral on Tuesday because she was suffering from acute sinusitis.
Prince William and Catherine will be part of a ceremonial welcome. There will also be a gun salute, military inspection and President Trump and First Lady Melania Trump will have a carriage procession within the Windsor estate.
Such spectacles will be aimed at pleasing a president who on Tuesday evening at Winfield House once again revealed his enthusiasm for royalty, saying about the King: "He's been a friend of mine for a long time, and everybody respects him, and they love him."
On his feelings about the UK, President Trump said: "I have a lot of things here that warm my heart. I want to tell you. It's a very special place."
A key message from the UK government will be to encourage the United States to maintain its commitment to Nato and to support Ukraine, and there will be a much bigger than usual military line-up for the state visit.
There will be 1,300 service men and women, from the Army, Royal Navy and RAF taking part in the welcome, creating the largest ever guard of honour for a state visit to the UK.
A joint US and UK flypast by F-35 jets and the Red Arrows will fly over Windsor, watched by Starmer alongside the president, in a display showing the closeness of the military relationship.
The centrepiece of the state visit will be the spectacular banquet in St George's Hall, where King Charles and President Trump will make speeches, with guests enjoying a menu that is likely to be a culinary representation of the special relationship, with UK and US food.
Along with the royal pageantry and photo-opportunities, there will be efforts to influence the US president over trade and international co-operation.
State visits are a form of soft power diplomacy, using the royal charm offensive to build relations with important international partners - with none more important than the US.
As the visit got under way, a major technology deal was announced with US tech firms investing £31bn in the UK, including £22bn from Microsoft.
This will see co-operation in artificial intelligence, quantum computing and nuclear power, in a tech deal which Sir Keir Starmer hopes will begin "creating highly skilled jobs, putting more money in people's pockets".
Trump had earlier said that the UK "want to see if they can refine the trade deal a little bit… I'm into helping them.
Ahead of the visit, the owner of Google, Alphabet, announced a £5bn ($6.8bn) investment in the UK's artificial intelligence research.
And an agreement is to be signed between the US and UK on accelerating the development of nuclear power.
But ambitions to remove the current 25% tariff on UK steel exports to the US seem to have been put on hold - although this remains lower than the 50% tariff facing many other countries.
Anti-Trump protestors begun to gather in Windsor on Tuesday - and giant images of Donald Trump and sex offender Jeffrey Epstein were projected on to the walls of Windsor Castle.
Thames Valley Police later said four men had been arrested following an "unauthorised projection" and remained in custody.
A heavy security operation will be in place during the presidential visit, which ends on Thursday afternoon.
But unlike other recent state visits, there will not be any moments visible to the public, with all the events taking place behind the walls of the Windsor estate or at the PM's country estate, Chequers.
The high street in Windsor has US flags flying, but they won't be seen by the visiting president.
Source : BBC