Celebrity Halloween Costume Pictures 2011 From Twitter

The Aussies who celebrated Halloween would've gone trick-or-treating yesterday, but the main event occurs in the US today. Many stars got a head start on the fun over the weekend, with red carpet events or parties, and the A-listers were also happy to share some of their own snaps online. We've collected photos from Nicole Richie, Nina Dobrev, Lea Michele, Derek and Julianne Hough, and many more — click through to see the images shared on Twitter!