Johnny Mercer contributed to five of Fred Astaire's thirty studio-era musicals: among songwriters, only Irving Berlin worked on a greater number of Astaire films. Always an aspiring songwriter, Astaire called upon Mercer as lyricist, co-composer and song doctor. This paper considers Mercer's many collaborations with Astaire, a body of work that extends across two decades and reaches beyond musical film to the parallel realms of popular recordings and television. Putting Astaire and Mercer in the same frame brings both men into focus in new ways. Both adjusted effectively to changes in the popular entertainment marketplace and showed particular sensitivity to shifts in musical style: thriving in the age of swing; sustaining their positions in the post-war "classic pop" era; finding new, if narrower niches after the rise of rock and roll. And both excelled at adapting black vernacular jazz idioms for mainstream (white) audiences. Looking at Astaire through his work with Mercer – and vice versa – brings a particular sharpness to the historical image of both of these creators of popular entertainment.