"Happy Birthday remains the most profitable song ever. Every year, it is the song that earns the highest royalty rates, sent to Warner/Chappell Music (which makes millions per year from 'licensing' the song). However, as we've been pointing out for years, the song is almost certainly in the public domain. Robert Brauneis did some fantastic work a few years ago laying out why the song's copyright clearly expired many years ago, even as Warner/Chappell pretends otherwise. You can read all the background, but there are a large number of problems with the copyright, including that the sisters who 'wrote' the song, appear to have written neither the music, nor the lyrics. At best, they may have written a similar song called 'Good Morning to All' in 1893, with the same basic melody, but there's evidence to suggest the melody itself predated the sisters. But, more importantly, the owner of the copyright (already questionable) failed to properly renew it in 1962, which would further establish that it's in the public domain.
The issue, as we've noted, is that it's just not cost effective for anyone to actually stand up and challenge Warner Music, who has strong financial incentive to pretend the copyright is still valid. Well, apparently, someone is pissed off enough to try. The creatively named Good Morning to You Productions, a documentary film company planning a film about the song Happy Birthday, has now filed a lawsuit concerning the copyright of Happy Birthday and are seeking to force Warner/Chappell to return the millions of dollars it has collected over the years. That's going to make this an interesting case."