The evening before Louis Armstrong recorded this album, both he and Miss Fitzgerald were appearing in an all-star concert also featuring Art Tatum and Oscar Peterson that was recorded for an album titled Live At The Hollywood Bowl (1956). The following day the two singers, along with the Oscar Peterson Trio, were in a Los Angeles studio to record this gem of an album.
With no time for rehearsals the songs were all set in Louis' key to make it easier, but this in no way inhibits Ella's performance. Another challenge for Pops was the fact that the material was not his normal repertoire, meaning he had to learn things on the fly in the studio. Again there's no hint of any issues, which all goes to highlight Armstrong's innate musical ability.