"Puttin' On the Ritz" is a song written by Irving Berlin. He wrote it in May 1927 and first published it in December 2, 1929. It was registered as an unpublished song August 24, 1927 and again on July 27, 1928. It was introduced by Harry Richman and chorus in the musical film Puttin' On the Ritz (1930). According to The Complete Lyrics of Irving Berlin, this was the first song in film to be sung by an interracial ensemble. The title derives from the slang expression "to put on the Ritz," meaning to dress very fashionably. The expression was inspired by the opulent Ritz Hotel.

Hit phonograph records of the tune in its original period of popularity of 1929–1930 were recorded by Harry Richman and by Fred Astaire, with whom the song is particularly associated. Every other record label had their own version of this popular song (Columbia, Brunswick, Victor, and all of the dime store labels). Richman's Brunswick version of the song became the number-one selling record in America.

The song is in AABA form, with a verse. According to John Mueller, the central device in the A section is the "use of delayed rhythmic resolution: a staggering, off-balance passage, emphasized by the unorthodox stresses in the lyric, suddenly resolves satisfyingly on a held note, followed by the forceful assertion of the title phrase." The marchlike B section, which is only barely syncopated, acts as a contrast to the previous rhythmic complexities. According to Alec Wilder, in his study of American popular song, for him, the rhythmic pattern in "Puttin' On the Ritz" is "the most complex and provocative I have ever come upon."

The original version of Berlin's song included references to the then-popular fad of flashily-dressed but poor black Harlemites parading up and down Lenox Avenue, "Spending ev'ry dime / For a wonderful time". In the UK, the song was popularized through the BBC's radio broadcasts of Joe Kaye's Band performing it at the The Ritz Hotel, London restaurant in the 1930s. The song was featured with the original lyrics in the 1939 film Idiot's Delight, where it was performed by Clark Gable and chorus, and this routine was selected for inclusion in That's Entertainment (1974). Columbia released a 78 recording of Fred Astaire singing the original lyrics in May 1930 (B-side – "Crazy Feet", both recorded on March 26, 1930). For the film Blue Skies (1946), where it was performed by Fred Astaire, Berlin revised the lyrics to apply to affluent whites strutting "up and down Park Avenue." This second version was published after being registered for copyright on August 28, 1946.

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