"Unforgettable" is a popular song written by Irving Gordon. The song was published in 1951.

The most popular version of the song was recorded by Nat King Cole in 1951, with an arrangement written by Nelson Riddle. A non-orchestrated version of the song recorded in 1952 is featured as a bonus track on the CD reissue of 1955's completely instrumental (save the bonus material) Penthouse Serenade. Cole again recorded the tune ten years later, in a stereo version recorded for the album The Nat King Cole Story. His version of the song was included extensively in the 2009 film Watchmen.

In 1991, Cole's 1962 recording of the song was edited and remixed to create a duet with his daughter, Natalie, which won three awards at the Grammy Awards of 1992: Song of the Year, Record of the Year and Best Traditional Pop Vocal Performance .

Nat Cole's original recording was inducted into the Grammy Hall of Fame in 2000.