You Stepped Out of a Dream was written by Nacio Herb Brown in 1940 for the film Ziegfeld Girl. The song uses a simple two part form and was originally in the key of D major. This is an analysis of the harmony in You Stepped Out of a Dream and an explanation of the concepts used in the analysis. The image above shows my full analysis, which I will explore in more detail below. You can refer to the conventions page to explore the analytic concepts used or get the PDF for free.
The A section begins on the I before shifting up a half step to the flat II major seventh. This is followed by a ii-V-I of flat VI, followed by a ii-V-I of IV. The A section ends with a ii-V of V before a sub V of V leading to the V7 dominant.
The B section starts the same way as A with the I moving up a half step to the flat II major seventh followed by the ii-V-I of flat VI. It changes on the 7th bar of B by going to the tritone substitution of the V of ii. This is followed by a II dominant leading to a I-iii-ii-V-I diatonic cadence at the end.