Justin Bieber, Miley Cyrus, Taylor Swift, Katy Perry, Carrie Underwood, Alicia Keys and Usher were just a few of the many A-listers on hand at tonight's Billboard Music Awards in Las Vegas. The show, hosted by "Modern Family" stars Julie Bowen and Ty Burrell, was held at the MGM Grand Garden Arena. Check out the full gallery of red-carpet arrival photos below!