Imagine writing a song that people around the world instantly know after the first couple of notes are played. Sisters Mildred Hill and Patty Smith Hill did just that.

Patty Hill was a young kindergarten teacher in Louisville, Ky., when she approached her sister Mildred, an accomplished pianists, about writing music for several songs she had written. Patty’s idea was to use songs as a method of instruction. In 1894, the Hill sisters published “Song Stories for the Kindergarten,” a collection of original songs.

One of those songs was “Good Morning to All,” which had the following lyrics:

Good morning to you

Good morning to you,

Good morning, dear children,

Good morning to all.

The melody for the song is what we know today as the “Happy Birthday to You” song. According to Robert Brauneis, the Happy Birthday lyrics began being used with the Hill sisters’ melody sometime after the turn of the century, though no one is exactly sure who originally changed the words. Between 1915 and 1935 “Happy Birthday to You” became the standard song people sang at birthday parties says Brauneis, an associate professor of law and the co-director of the Intellectual Property Law Program at George Washington University Law School. In fact, the very first singing telegram on July 28, 1933 featured “Happy Birthday to You” Brauneis notes.

Despite the popularity of the song, the Hill sisters are just a footnote in history, primarily because of copyright dispute. “Song Stories for the Kindergarten” was published by the Summy Co. In 1935, the company applied for and received a copyright for “Happy Birthday to You,” even though the Hill sisters’ melody was co-opted for the song.

Through the years, both the Summy Co. and the copyright to the song were sold. Warner Music Group currently holds the copyright, which expires in 2030. Brauneis doubts the legitimacy of the copyright, and lays out his case in a 68-page paper with more than 300 footnotes titled “Copyright and the World’s Most Popular Song.” That hasn’t stopped Warner from collecting royalties. And restaurants like Red Lobster and Outback Steakhouse have created their own birthday songs specifically to avoid any copyright dispute with Warner.

Did you know?

In 1996 the American Society of Composers, Authors and Publishers [ASCAP], the organization that collects royalties for copyrighted songs, demanded the Girl Scouts pay royalties for singing “Happy Birthday to You” around campfires. Public outcry forced ASCAP to back down from its demands.

In the late 1940s, “Happy Birthday to You” generated about $15,000 per year in royalty revenue. Today the song brings in about $2 million annually.