Christina Milian, Justin Bieber

Though it's easy to write off much of today's pop music as auto-tuned bubblegum, stars like Beyonce and Mariah Carey take great pride in the fact that they write many their own songs. And you might be surprised to learn that some of today's chart toppers not only write their own music, they've also had a hand in the major success of their fellow artists' careers. We've got 8 behind-the-scenes big names that have penned tunes for everyone from Rihanna to Justin Bieber.