"Things Ain't What They Used to Be" is a 1942 jazz standard with music by Mercer Ellington and lyrics by Ted Persons.
In 1941 there was a strike against the American Society of Composers, Authors and Publishers, of which Duke Ellington was a member.
[1] Strayhorn's compositions of this time include "Take the 'A' Train", "Chelsea Bridge" and "Day Dream".
Mercer wrote "Things Ain't What They Used to Be", "Blue Serge" and "Moon Mist".
[2] Jazz musician and historian Chris Tyle argues that most likely Mercer Ellington came up with the melody and his father then arranged the song for the band.