Everyone knows Happy Birthday. We sing it at parties, at school and at home. But here's the strange thing… who actually wrote it? The tune was created by two American sisters, Mildred and Patty Hill, in the 1890s. They wrote a song called Good Morning to All for children to sing at school. Later, the words somehow changed to Happy Birthday to You. But nobody knows for certain who wrote the birthday words! The song became incredibly popular and, for many years, people believed that someone owned the rights to it. That meant people sometimes had to pay to use it. Eventually, a court decided that the copyright claim was not valid. So the song we all sing has a surprisingly mysterious history!