The Queen will celebrate her birthday at Windsor Castle today.
A traditional 41 gun salute will be fired in Green Park, London by the King's Troop Royal Horse Artillery at midday.
An hour later, the Honourable Artillery Company will fire a 62 gun salute from the Tower Wharf by the Tower of London.
To mark her 88th birthday, a portrait by British photographer David Bailey has been released.
The picture was taken in March and commissioned on behalf of the Government's GREAT Britain campaign.
The Queen has two birthdays, her actual one is today whilst her official one is in June.
Her birthday in June is celebrated with the Trooping the colour parade.
Ireland's President Michael Higgins today praised the "warm friendship" with the UK as he became the first Irish head of state to address the House of Parliament.
Mr Higgins said the links between the two countries were now "strong and resolute" and there was now "mutual respect" despite historical differences.
The Queen and the Irish President Micheal D Higgens have been viewing Irish items in the Royal collection in Windsor as part of the historic state visit.
President Higgins will address the Houses of Parliament later this afternoon, before the royal banquet this evening.
Irish President Michael Higgins has made history today by becoming the first ever Irish President head of state to visit the UK.
He was greeted by the Queen and Duke of Edinburgh at Windsor Castle today along with his wife Sabrina Higgins.
The Queen and the President of Ireland stood side by side to observe the Irish Anthem being played by a military band in Windsor, during the first visit to the UK by an Irish head of state.
The anthem was played after the President Higgins and Michael Higgins were honoured with two separate gun salutes, and Mr Higgins and Philip inspected troops of the Queen's Company, Genadier Guards.
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. The Irish Guards was represented by their regimental band as the troops are currently on peacekeeping duties in Cyprus.
President Higgins presented a new ceremonial red coat to its regimental mascot, an Irish wolfhound called Domhnall of Shantamon.