The first visit by a British monarch in 100 years continued today amid the biggest ever security operation in the history of the State.
As Queen Elizabeth II signed the visitor’s book at Aras an Uachtarain at lunchtime, the Duke of Edinburgh joked: “Do you want me to put the date on it?”.
The royal flight touched down on schedule just before midday for the start of the historic four-day visit which signals a new era in Anglo-Irish relations.
The sovereign - wearing a green hat and coat - and the Duke of Edinburgh were escorted down the red carpet at Baldonnel aerodrome to a motorcade, past an Irish Air Corps guard of honour to accept flowers from eight-year-old Rachel Fox, from Dun Laoghaire, Co Dublin.
The royal couple were also greeted off the plane by British Ambassador Julian King, Ireland's Ambassador to the UK Bobby McDonagh and Tanaiste Eamon Gilmore.
The royal couple were then driven to President Mary McAleese's residence in the Phoenix Park, Aras an Uachtarain, for a ceremonial welcome.
The escort included 33 green Honda motorbikes with green, red and black tricolour flags for the Second Cavalry Squadron, representing the 32 counties of Ireland, plus one with the Union flag.
At the gates leading to the Aras the Irish Tricolour and Union flag flew side by side.
The hallway to the ballroom in the president's residence, where the Queen signed a visitor’s book, was also lined with the flags of the two states.
The Queen was introduced to Taoiseach Enda Kenny at the Aras and had a private meeting with the President before lunch.
One of the monarch's first official engagements this afternoon was a wreath-laying ceremony at the Garden of Remembrance in Dublin city centre which honours all those who fought for Irish freedom from British rule.
Up to 6,000 police and soldiers were on duty across the capital as part of unprecedented measures to protect the royal couple and thwart any possible attack by dissident republicans, who also plan to stage a number of protests in the capital, one close to the Garden of Remembrance.
There were several security alerts in the city today including one in the north Dublin shortly before the monarch's plane touched down.
There were also threats made forcing courthouses to be searched and cleared in Dundalk, Monaghan and Drogheda. No explosive devices were found.
The Queen shook hands with the President at the front of the Aras before moving inside to be greeted by Taoiseach Enda Kenny and sign the visitors' book.
God Save The Queen and Amhrann na bhFainn, the Irish national anthem, were played in the grounds of the Aras as a 21-gun salute sounded and an Air Corps flypast took place.
The Queen reviewed the guard of honour before joining the Duke in a private meeting with the President and her husband, Dr Martin McAleese.
To sign the visitor's book, the Queen sat down in the Aras's lavish state ballroom, which dates from 1802.
She arrived with the President looking relaxed and the two women, who have met a number of times before, chatted animatedly. They were followed by the Duke and Dr McAleese.
Under an ornate Regency-style brass chandelier commemorating the Act of Union of 1801 with an intertwining shamrock, rose and thistle - the national floral emblems of Ireland, England and Scotland - the Queen took off her right black glove and picked up a pen to write her signature.
Philip took his own pen from his pocket and joked with the group, asking: "Do you want me to put the date on it?"
The Queen choose a jade green coat to mark her visit in the first symbolic gesture of what will be an unprecedented and dramatic stay in the state.
On official trips the Queen often compliments host nations by incorporating national colours or emblems.
British Prime Minister David Cameron today stressed the "genuine friendship" between Britain and Ireland as Queen Elizabeth II was about to make her historic visit to this country.
But he also highlighted the "hard-headed business" interest between the two nations, citing that the UK did more trade with Ireland than with Brazil, Russia and India combined.
"There are some six million people with Irish grandparents in Britain with three million people travelling either way between the countries on an annual basis."
He added: "this is the start of something big."
Taoiseach Enda Kenny today joined the chorus welcoming Queen Elizabeth II to Ireland.
Speaking on Morning Ireland Mr. Kenny stated that he had "no difficulty" with people who planned to protest but appealed to any protestors not to embarrass the country during her stay.
He wasn't aware if the Queen's speech would contain an apology to Ireland, but was looking forward to hearing what she had to say during her address in Dublin Castle tomorrow evening.
Army bomb disposal experts early today dealt with a viable explosive device found on a Dublin-bound bus on the eve of the royal visit.
Police are patrolling the streets, parking is prohibited in many areas and large swathes of the city have been closed off.
Up to 30 passengers had to be evacuated after gardai stopped the bus in Maynooth, Co Kildare, at 9.30pm.
The incident followed an anonymous call to gardai in Longford that a device was on board the 5.45pm Ballina to Dublin bus.
Three garda cars stopped the bus on the Straffan Road near the railway station and immediately evacuated everybody on board the vehicle, which was being run by a private operator for Bus Eireann.
Gardai sealed off the surrounding area and warned residents to stay indoors.
A three-mile stretch of the road was shut down and an Army bomb disposal team arrived at the scene at about 11.30pm.
The pipe bomb, which was described as viable, was still being made safe at 1am this morning before being examined by garda forensic experts.
The discovery of the explosive device came after a coded bomb threat by the Real IRA in London sparked fears that a similar warning here could create a security nightmare for this week's visit by Queen Elizabeth.
The caller issued a recognised codeword used in the past by the dissident republican gang and it led to a five-hour shutdown near Buckingham Palace yesterday morning.
Senior garda officers said last night the alert in London underlined the need for the strict measures being implemented here to protect the queen during her four-day visit.
Scotland Yard believes the threat call was made from the Republic but had not pinned down the location last night.
Last month a masked member from the Real IRA declared its opposition to the visit at a rally in Derry and threatened to kill more police officers. It was responsible for the murder of two soldiers at Massereene Barracks in Antrim in March 2009.
The security alert in London was based mainly around The Mall, although the call, which was made on Sunday night, did not specify a time or a location.
It was the first coded warning by dissident republicans in London for more than a decade.
Now garda anti-terrorist officers are concerned that a similar attempt will be made today in a bid to create chaos during the queen's visit.