The Queen welcomed US President Donald Trump and First Lady Melania Trump at the Buckingham Palace on the first day of their state visit to the UK, the BBC reports.
After a private lunch, the couple will be given a tour of Westminster Abbey and will also join Prince Charles and the Duchess of Cornwall for tea at Clarence House.
Later, the Queen will host a state banquet at Buckingham Palace, also attended by the Duke and Duchess of Cambridge.
Within the framework of the visit, Trump is expected to discuss climate change and Chinese technology firm Huawei during talks with outgoing Prime Minister Theresa May.
The two leaders are also expected to discuss Huawei. The US has blacklisted the Chinese firm for security reasons, while the UK may allow it to supply "non-core" components for its 5G network.