The song Happy Birthday is in the public domain, a federal judge ruled yesterday.

The lawsuit against Warner/Chappell was filed back in 2013 by filmaker Jennifer Nelson and TV production company Good Morning To You Productions, which stated that the publisher’s copyright over the world’s most popular song was invalid.

The song dates back to a late 19th century work by a schoolteacher Patty Smith Hill and her sister Mildred Hill. The two assigned rights to a publishing company owned by Clayton Summy, which ...