8 April 2014
Last updated at 16:01 ET
Prince Charles met Irish President Michael D Higgins at the Irish Embassy in London to welcome him to the UK on the first state visit by an Irish head of state. Ahead of the visit, Mr Higgins said it would be be "very important for the relationships between the people of Ireland and UK".
Prince Charles escorted Mr Higgins to Windsor, where he met the Queen and the Duke of Edinburgh in the town. It was the Queen's visit to Ireland three year's ago which paved the way for Tuesday's historic event.
A town crier marked the historic occasion.
The Queen and Mr Higgins travelled in a procession to Windsor Castle, where the British and Irish national anthems were played.
At the castle, Mr Higgins received a ceremonial welcome.
A Sinn Fein MP said the state visit was a "symbolically significant step" on the "journey towards reconciliation and better relationships".
The Queen and Mr Higgins, who shared a carriage to Windsor Castle, sat side by side to watch soldiers march and rise past.
Hundreds of British Army troops are involved in the visit. Major Andrew Seddon, captain of the Queen's Company Grenadier Guards, invited Mr Higgins to inspect the guard of honour, speaking to him in Irish.
Mr Higgins presented a ceremonial coat to the Irish Guards for their Irish wolfhound mascot. It mirrored a gesture of friendship made 40 years ago, when, on St Patrick's Day in 1973, the Irish Guards gave a similar coat to the mascot of the Fifth Battalion of the Irish Army.
At Windsor Castle, the Queen showed Mr Higgins selected items relating to Ireland from the Royal Collection.
Mr Higgins and his wife Sabina then travelled to London and stopped in Westminster Abbey to look at a memorial to the Queen's cousin, Earl Mountbatten of Burma, who was killed by an IRA bomb.
Mr Higgins addressed both Houses of Parliament, speaking of the "warm, deep and enduring friendship" between Ireland and the UK.
Speaking at a banquet at Windsor Castle on Tuesday evening, the Queen said she was “delighted” to welcome Mr and Mrs Higgins. She said Britain and Ireland were “walking together towards a brighter and more settled future” and proposed a toast to Mr and Ms Higgins and “the health and prosperity of the people of Ireland”.