Queen lays wreath on Republic of Ireland state visit
The Queen, dressed in Irish green, finally set foot on Irish soil at 1203 BST.
It was one small step for the Queen - one huge moment in British-Irish history.
It is 100 years since a British monarch has been in Ireland. Many thought a king or queen would never be welcomed back.
Instead, Ireland rolled out the red carpet for her nearest neighbour.
The Queen has laid a wreath at the Republic of Ireland's Garden of Remembrance during the first visit to the country by a British monarch.
The act is significant as the garden, in Dublin, is dedicated to people who fought for Irish independence.
Dozens of protesters gathered nearby amid one of the biggest ever security operations in the country.
Earlier, the Queen was welcomed by President Mary McAleese after flying into Baldonnel military airbase.
It emerged that a pipe bomb found on a bus bound for Dublin on Monday had been made safe by the Irish army.
Upon landing at the military airbase, just outside Dublin, the Queen emerged wearing an outfit of symbolic emerald green.
After lunch the monarch wore a white outfit.
God Save The Queen was played when she arrived at the Garden of Remembrance to lay the wreath - regarded as a highly symbolic act as the garden commemorates Irish people who fought over the centuries against British rule.
A one-minute silence followed the laying of the wreath, after which the Irish Tricolour was raised from half to full mast and the country's national anthem was played.
Much of the centre of Dublin was cordoned off, leaving many streets empty, as part of the strict security clampdown put in place for the visit.
Meanwhile, riot police officers jostled with demonstrators at two separate protests on streets several hundred yards from the garden.
The sounds of protesters could be heard during the laying of the wreath and black balloons were released by some demonstrators.
There were scuffles between police and republicans protesting against the visit in the centre of Dublin at Tuesday lunchtime.
Up to 200 supporters of the Eirigi socialist republican party later retreated to stage a rally nearby.
The Queen then went on to Trinity College to be shown the Book of Kells, an ancient illuminated manuscript in Latin, containing the four gospels of the New Testament.
Later, the monarch met Trinity scholars, musicians and artists.
At Baldonnel airbase, the royal party was greeted by an Irish Air Corps guard of honour and presented with flowers by a south Dublin schoolgirl, eight-year-old Rachel Fox.