"The song "Happy Birthday to you" was written by two sisters from Kentucky. Mildred and Patty Smith were school teachers, and the song was actually originally "Good Morning to You" published in 1893. The lyrics were later changed and a copy rite law suit battle ensued led by a third Smith sister after the Happy birthday version was published in 1924, her fight didn't end until 1934, but her copy rite now stands and will stand until 2030.4 The popularity brought on another common custom of birthday parties, the writing of "Happy Birthday" on the cake. This was not done until the songs appearance. A lesser known custom of wiping the name of the person whose birthday it is from the cake, runs back to the origins of the birthday party, and is said to bring the person good luck. 5"

You can find more trivia about birthdays in my article in source. (Yes I am the author.)

Edit to add the sources tied to those numbers from the article lol since your requested sources from another answerer.
4. Snopes birthday song (http://www.snopes.com/music/songs/birthday.asp)
5. History of the Birthday cake (http://www.tokenz.com/history-of-birthday-cake.html)

From what I understand it originated in 1883 in Lousiville. It was like a classroom welcome. It was made in 1853 but was published in 1883. And another cool little fact was in the 80's the songs annual revenue was roughly 1 million dollars. Hope that helps some!

Hello, you know, after all this time I have never even thought about it! I just sing the dang song! lol
I checked into it though, apparently it is the most well recognized english song, which the base lyrics have been translated into 18 different languages.
The Melody itself is based on the song " Good Morning To All " Which was written by American sisters, Patty Hill and Mildred J Hill in 1893. They were both kindergarten teachers in Louisville Kentucky.
"Good Morning to All"
Good morning to you,
Good morning to you,
Good morning, dear children,
Good morning to all.

"Happy Birthday" first appeared in print in 1912, but not until 1935 did the Summy Company register for the copyright on it. In 1990 Warner Chappell the company owning the copyright for 15 million USD with the value of "Happy Birthday" being worth 5 million USD. This copyright will not expire until 2030...so start saving and perhaps you can own legal rights to the song ;).

Maybe this is why the Beatles came out with their own Birthday Song...give us an option in what to sing without having to pay royalties. :)
http://www.youtube.com/watch?v=MjF1bG5LUcs

Actually what I heard a long time ago is that 2 older ladies came up with the song and they used to get royalties every time it was played on TV or any where else a paying crowd was assembled.

"The origins of "Happy Birthday To You" date back to the mid-nineteenth century, when two sisters, Patty and Mildred J. Hill, began singing the song "Good Morning To All" to their kindergarten class in Kentucky. In 1893, they published the tune in their songbook Song Stories for the Kindergarten. However, many believe that the Hill sisters most likely copied the tune and lyrical idea from other songs from that time period.needed There were a number of popular and substantially similar nineteenth-century songs that predated the Hill sisters' composition, including Horace Waters' "Happy Greetings to All"; "Good Night to You All", also from 1858; "A Happy New Year to All", from 1875; and "A Happy Greeting to All", published 1885. The copyright for both the words and the music of "Good Morning to All" has since expired and both are now a part of the public domain.
The Hill Sisters' students enjoyed their teachers' version of "Good Morning To All" so much that they began spontaneously singing it at birthday parties, changing the lyrics to "Happy Birthday". In 1924, Robert Coleman included "Good Morning to All" in a songbook with the birthday lyrics as a second verse. Coleman also published "Happy Birthday" in The American Hymnal in 1933. Children's Praise and Worship, edited by Andrew Byers, Bessie L. Byrum and Anna E. Koglin, published the song in 1928.
In 1935 "Happy Birthday to You" was copyrighted as a work for hire by Preston Ware Orem for the Summy Company, the publisher of "Good Morning to All". A new company, Birch Tree Group Limited, was formed to protect and enforce the song's copyright. In 19988, the rights to "Happy Birthday to You" and its assets were sold to The Time-Warner Corporation. In March 2004, Warner Music Group was sold to a group of investors led by Edgar Bronfman Jr. The company continues to insist that one cannot sing the "Happy Birthday to You" lyrics for profit without paying extremely high royalties: in 2008, Warner collected about $5000 per day ($2 million per year) in royalties for the song.2, pp. 4,68 This includes use in film, television, radio, anywhere open to the public, or even among a group where a substantial number of those in attendance are not family or friend to whoever is performing the song.
Except for the splitting of the first note in the melody "Good Morning to All" to accommodate the two syllables in the word "happy", "Happy Birthday to You" and "Good Morning to All" are melodically identical. Precedent (regarding works derived from public domain material, and cases comparing two similar musical worksneeded) seems to suggest that the melody used in "Happy Birthday to You" would not merit additional copyright status for one split note. Whether or not changing the words "good morning" to "happy birthday" should be covered by copyright is a different matter. The words "good morning" were replaced with "happy birthday" by others than the authors of "Good Morning to All". Regardless of the fact that "Happy Birthday to You" infringed upon Good Morning to All, there is one theory that because the "Happy Birthday to You" variation was not authored by the Hills, and it was published without notice of copyright under the 1909 U. S. copyright act, that the 1935 registration is invalid.
Many question the validity of the current copyright, as the melody of the song was most likely borrowed from other popular songs of the time, and the lyrics were improvised by a group of five and six-year-old children who never received any compensation. The song is currently set to pass in to the public domain in 2030."

Strange....
Almost everyone in this world, irrespective of any nationality, sing this "Happy Birthday " song on our dear one's Birthday. Thanks to Patty Hill & Mildred Hill, the two sisters who are said to be the origin of this tune, way back in 1893. Both the sisters sung the song in their Kindergarten Class in Louisville, Kentucky for their students while developing some new and interesting teaching skills. They later on also published the same along with some other tunes & songs ( like Good Morning to all, Happy Greetings to all & so on.. ).

Since then various artists published the song with different lyrics and a bit changed tune, but the tune was finally copywrited in 1935 by Preston Orem ( of Summy Company ) only uptil 1998, after which in the same year the copyrights for the song and its assests were sold to The Time Warner Corporation. Again in 2004, The Warner Music Group was sold to a group of investers which have the copyright authority and insist that one cannot use the tune and sing the lyrics for profit without paying the royalties.

From a simple Kindergarten School song, this "Happy Birthday " song has become one of the most widely used common english songs in the world. According to the Guinness Book of World Records (1998), " Happy Birthday to you " is the most recognised English song in the world & the song's base lyrics has known to be translated in 18 languages world wide...

Once again... Thanks to the Hill sisters for coming up with such a sweet thought and tune...