Happy Birthday to You, the four-line ditty was written as a classroom greeting in 1893 by two Louisville teachers, Mildred J. Hill, an authority on Negro spirituals, and Dr. Patty Smith Hill, professor emeritus of education at Columbia University.

The melody of the song Happy Birthday to You was composed by Mildred J. Hill, a schoolteacher born in Louisville, KY, on June 27, 1859. The song was first published in 1893, with the lyrics written by her sister, Patty Smith Hill, as “Good Morning To All.”

Happy Birthday to You was copyrighted in 1935 and renewed in 1963. The song was apparently written in 1893, but first copyrighted in 1935 after a lawsuit (reported in the New York Times of August 15, 1934, p.19 col. 6)

In 1988, Birch Tree Group, Ltd. sold the rights of the song to Warner Communications (along with all other assets) for an estimated $25 million (considerably more than a song). (reported in Time, Jan 2, 1989 v133 n1 p88(1)

In the 80s, the song Happy Birthday to You was believed to generate about $1 million in royalties annually. With Auld Lang Syne and For He’s a Jolly Good Fellow, it is among the three most popular songs in the English language. (reported in Time, Jan 2, 1989 v133 n1 p88(1)

Happy Birthday to You continues to bring in approximately 2 million dollars in licensing revenue each year, at least as of 1996 accounting, according to Warner Chappell and a Forbes magazine article.

(via http://www.ibiblio.org/team/fun/birthday/)