Irish President Michael D Higgins will meet the Queen at an official banquet held at Windsor Castle as his state visit to the UK begins.
The president and his wife, Sabina, will be the guests of the Queen and the Duke of Edinburgh at Windsor Castle for the four-day visit.
Northern Ireland's deputy first minister, Martin McGuinness, who did not meet the British monarch during her Dublin visit, will be present for the state banquet, along with amongst others, First Minister Peter Robinson, Prime Minister David Cameron and Taoiseach (Irish prime minister) Enda Kenny.
This is the first state visit by a head of the Irish state and marks the "maturity and warmth" which has grown between the two countries, Mr Higgins wrote last week.
Queen Elizabeth was the first British monarch to visit Ireland in May 2011.
Michael Higgins is the first Irish President to make a state visit to the UK, ending the day with a state banquet at Windsor Castle.
Today's historic visit is a symbolic ending to the painful separation of British and Irish states, but 3000 unsolved murders remain.