"What a Diff'rence a Day Made", also recorded as "What a Difference a Day Makes", is a popular song originally written in Spanish by María Grever, a Mexican songwriter, in 1934 with the title "Cuando vuelva a tu lado" ("When I Return to Your Side") and first recorded by Orquesta Pedro Vía that same year.

A popular version in Spanish was later recorded by trio Los Panchos with Eydie Gormé in 1964.

[4] The English lyrics were written by Stanley Adams, and was played by Harry Roy & his Orchestra.

[5] Dinah Washington won a Grammy Award in 1959 for Best Rhythm and Blues Performance with this song.

Phillips performed the song on the television comedy variety program Saturday Night Live during its first season.