"Happy birthday to you"

"Happy birthday to you" is [quite obviously] a song which is sung to celebrate the anniversary of a person's birth.

The melody of "Happy birthday to you" was written by two sisters, Patty and Mildred Hill, in Louisville, Kentucky. One day, in 1893, while Mildred was teaching at the Louisville Experimental Kindergarten School where her sister served as principal, she came up with the modest melody. Patty added some simple lyrics and completed the creation of "Good Morning to All," which was originally intended as a simple greeting song for teachers to use in welcoming students to class each day.
But nobody really knows who wrote the words to "Happy birthday to you" and put them together with the sister Hills' melody, or when it happened.

The ownership of the song has swapped hands many times : the copyright is currently owned by Time Warner but is scheduled to expire in 2030. For more information regarding the copyright issue, see : http://www.snopes.com/music/songs/birthday.htm.

Though the song is copyrighted, you do have the right to sing it your friends or family, in a private home.
One of the most famous performances of "Happy birthday to you" was Marilyn Monroe's rendition to U.S. President John F. Kennedy in May 1962. Did she engage in copyright infringement by doing that ?
Available in your head : who doesn't know that song ?