Hobbit Day is the birthday of the hobbits Bilbo and Frodo Baggins, two fictional characters in J. R. R. Tolkien's popular set of books The Hobbit and The Lord of the Rings. In the books both Bilbo and Frodo were said to be born on September 22, but of different years. Bilbo was born in the year of 2890 and Frodo in the year of 2968 in the Third Age (1290 and 1368 respectively in Shire-Reckoning.)
Tolkien Week is the week containing Hobbit Day.
The American Tolkien Society first proclaimed Hobbit Day and Tolkien Week in 1978, and defines them as this: "Tolkien Week is observed as the calendar week containing September 22, which is always observed as Hobbit Day", but acknowledges that Hobbit Day pre-dates their designation.
Due to the discrepancies between the Shire calendar and the Gregorian calendar there is some debate about when to celebrate Hobbit Day, since the actual birthday would be between September 12 and 14 the Gregorian calendar, as explained in the appendices of The Lord of the Rings.
The Fellowship of the Ring opened with a celebration of Bilbo's birthday. It was a large party with food, fireworks, dancing and much merriment.
Some Tolkien fans celebrate by having parties and feasts emulating the hobbit's parties. Other fans celebrate by simply going barefooted in honor of the hobbits, who don't wear shoes.
Some schools and libraries use this as an opportunity to pique interest in Tolkien's work by putting up displays and hosting events.
According to The Lord of the Rings appendices, "There is no record of the Shire-folk commemorating either March 25 or September 22; but in the Westfarthing, especially in the country round Hobbiton Hill, there grew a custom of making holiday and dancing in the Party Field, when weather permitted, on April 6."