Songfacts®:

• Astaire performed this in the 1948 movie Easter Parade, and his became the most famous version of the song. It was written by Irving Berlin, who used the melody of a song he wrote in 1917 but never caught on called "Smile And Show Your Dimple." Writing new lyrics to old melodies was common practice for Berlin, who also did it with "God Bless America."
• Berlin wrote this for his 1933 stage show As Thousands Cheer. The song became much more popular after Astaire and Judy Garland sang it in the movie.
• According to Mark Steyn's A Song for the Season, Berlin was struggling to create the perfect song to accompany the Act One finale for As Thousands Cheer - a scene where figures come to life from a sepia photograph. "We wanted a big Fifth Avenue number," said Berlin. "I wanted an old-fashioned type song, but I couldn't come up with anything."
  
  Then he remembered the first four bars of "Smile and Show Your Dimple": "So, instead of try to write a new old-fashioned melody I simply used a real old-fashioned melody. Except that now, of course, I made the words apply to an Easter parade."
• "A song is like a marriage," Berlin explained. "It takes a perfect blending of the two mates, the music and the words, to make a perfect match. In the case of 'Easter Parade,' it took a divorce and a second marriage to bring about the happiest of unions."