A: It's a celebration named for Leopold and Molly Bloom, James Joyce's iconic protagonists of his masterpiece, Ulysses, which takes place over a 24 hour period on June 16th 1904; 106 years ago today.
Q: OK. so how do people celebrate this anniversary?
A: Well if you live in Dublin, where the book is set, there is a week-long celebration, The Bloomsday Festival.
In other cities like New York for example, there are many activities set. The New York City activities are listed at BLOOMSDAYnyc.
Q: What goes on at these celebrations?
A: Mostly readings from the novel but also tours, pub crawls, concerts featuring Irish music, and, yes, there will be Guinness.
Q: Why is this post written in the question and answer format?
A: It is a clever spoof of the novel, Ulysses, in which one entire chapter is related through questions and answers.