A US judge (George King) has ruled that Warner/Chappell, which acquired the copyright to Happy Birthday in 1988, only bought rights to specific arrangements of the melody, not to the actual song. Warner/Chappell got the rights when it bought another company, which was the successor to yet another company, which got the rights from sisters Mildred and Patty Hill, who wrote the song Good Morning to All in 1893. That song was meant to be sung in class by school children, and the melody was later combined with the Happy Birthday lyrics that we know today. If you’re as confused as I am, then you’re getting a glimpse at the mess which is current copyright law.
This judgement applies only to the US, and only to part of the song. Other parts of the song and other renditions of it may still be encumbered, so think twice before posting your birthday party on Youtube if it contains any part of the Happy Birthday song. Read the linked articles for more clarificatioon.
A small step in the right direction, since this song might finally be kinda, sorta, partially in the public domain at last.