St Patrick's Day is celebrated around the world on 17 March. The day marks the arrival of Saint Patrick to Ireland as a missionary. The saint played a prominent role in converting Celtic pagans to Christianity. Legend has it that he also drove all the snakes out of Ireland. The country remains snake-free to this day, apart from the occasional pet.
Many countries around the world, as far afield as the United States, Denmark, Argentina and Japan, celebrate the day with parades, green-coloured beer and - of course - green costumes.
"Happy St Patrick's Day" has been trending on Twitter, with people sending their wishes and detailing plans for the day.
"@amyd1987 Happy St.Patricks Day everyone! I'll be celebrating by watching the best Irish band ever @thescript at the M.E.N! Can't frickin' wait!!!"
"@MattBerryMB Happy St. Patricks Day. Start drinking breakfast at a quarter to ten? Check. Be in a parade? Check. Gonna be a good day."
"@AntRogJr Happy st.patricks day everyone wear ya green today or get pinch and have a great day."
"@Tanisha_O words cannot describe my excitement for tonight .. @NiallOfficial , Happy St Patricks Day! #onedirectioninliverpool"
"@thatvintagebird Roses are red, Shamrocks are green, Come down to @BikeBoutiqueLdn, Coz it's march seventeen!!! Happy St Patricks Day"
"@seldomseentrev Happy St Patricks Day to all my US friends who think they're Irish, English friends who wish they were Irish and Irish friends who know."
"@thatgirl_JAN "Thanks a million" & "A pint of bitter" - my fav Irish sayings. A tad stereotypical but hey....love the Irish. Happy St Patricks Day!"
"@AnonDCC Let the green colors commence! Show off that green-anarchy that is so precious and beutiful~ idk happy st.patricks day #occupygresham #opdx"
"@PopePolar Happy St Patricks Day - Great #Green #Aurora happening right now. Our solar system is evidently Irish."
"@lwyerx Happy St Patricks Day, what could be more delightful than some homework and football? #WesHoolahan "
St Patrick's Day is one of the world's most widely celebrated saints' days and shows the best and brightest of Irish tradition and culture. Interestingly, the colour first associated with St Patrick was blue but over the years green grew in popularity, thanks to Ireland's nickname - The Emerald Isle.
According to legend, St Patrick used the shamrock - a three-leaved plant - to explain the Holy Trinity. Hence, shamrocks and shamrock-inspired designs have become a significant part of the day.