"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. The song is also known in English as "What a Diffrence a Day Makes", as popularized by Dinah Washington in 1959. The English lyrics were written by Stanley Adams and were first played by Harry Roy & his Orchestra. It was published in late 1934. The most successful early recording, in 1934, was by the Dorsey Brothers, although it was first recorded in English by Cleveland crooner Jimmy Ague.

Dinah Washingtons version of the song was released in 1959 and became a hit. The song has been covered by many artists over the years, including Lonnie Johnson, Little Anthony and the Imperials, and Bobby Darin.

In 2021, artist and songwriter SHELLS and producer Robin Pearkes (aka PALMR) recorded an English version entitled "What a Difference a Day Makes". It was commissioned for the UKs National Health Service (NHS) .

"What a Difference a Day Makes" is a song about the transformative power of love. The lyrics describe how a single day can change everything, from the weather to ones emotional state. The song has become a classic and is still enjoyed by many people today.