When you imagine Saint Patrick's Day in your mind's eye, its always the colour green that comes to mind. But initially blue was the colour associated with St Patrick - and Ireland by extension. In fact the shade of blue was known as St Patrick's Day Blue. Due to its links with the shamrock, green began to supplant blue in Saint Patrick's Day celebrations the 1600s.

St Patrick's Day became a public holiday in Ireland, 110 years ago thanks to an Irish MP James O'Mara. He was also responsible for a law which required pubs to close on March 17th to prevent public drunkeness. That law was not repealed until the 1970s.

Although Saint Patrick's Day is traditionally held on March 17th, back in 2008 it was held a couple of days early after a decision by bishops because it coincided with Holy Week. Holy Week and St Patrick's Day will not clash again until 2160 - so there's time yet to choose another date if required.

In the tiny Carribean island of Montserrat, Saint Patrick's Day is a public holiday because it was founded by Irish refugees from the neighbouring island of St Kitts and Nevis. Known as the 'Emerald Island of the Carribean', it is one of just two places outside Ireland which consider March 17th to be a public holiday.

The tradition of presenting a bowl of Shamrocks to the US President began in 1952 during the Presidency of Harry Truman as a means of strengthening ties. But Truman was not hand to receive the gift that year, so the Irish ambassador John Joseph Hearne simply dropped off a box of shamrocks at the White House.