The movie pays a long-overdue tribute to their glorious pipes, but also engages with the disconnection between talent and stardom, and while it isn't exactly an exposé of the music industry, infuriating details emerge.

Artists including Mick Jagger talk about their backing singers -- and the soundtrack is, of course, heavenly.

While there are moments in the film awkwardly placed to achieve moments of pensiveness from the talent, what it does well is offers a point of view where there wasn't before.

The poster... advertises the appearances of Bruce Springsteen, Sting, Mick Jagger, Stevie Wonder and Bette Midler, ironic since the documentary is really about the back-up singers who performed with them and many others, always outside of the spotlight.