King Abdullah of Saudi Arabia is making the first state visit to the UK by a Saudi monarch for 20 years. However, his trip is not without controversy.
The Queen, along with the Duke of Edinburgh and Prince Charles, gave a ceremonial welcome to the king.
Captain of the Guard, Major Ben Ramsay, invited the king - in Arabic - to review the 1st Battalion Welsh Guards.
Members of the king's travelling party watched on with interest at the formalities taking place on Horse Guards Parade.
Prime Minister Gordon Brown, Minister for the Middle East Kim Howells and Home Secretary Jacqui Smith were among the dignitaries present for the king's arrival.
Prince Charles's attention is caught by demonstrators who gathered on The Mall to protest over human rights and the arms trade.
The king headed the short distance to Buckingham Palace in the Australian state coach. The Queen will host a banquet at the palace in honour of the king.