Kim Kardashian and Jonathan Cheban dressed up as Sonny and Cher. Kardashian, who said her costume theme this year was her favorite icons, also dressed up as Aaliyah and as Madonna, while Kourtney dressed up as Michael Jackson.
Demi Lovato went as late Tejano singer Selena.
But other celebrities went for a more fantastical costume, like Paris Jackson.
Frozen's own Princess Anna went as Elsa because, Kristen Bell wrote, her daughter insisted.
Adele left fans guessing what her fabulous green ensemble was meant to be.
Here are more of the best celebrity costumes so far.
Cindy Crawford and Rande Gerber as That '70s Show
Jason Derulo as the Night King from Game of Thrones
Usher as Jules Winnfield from Pulp Fiction
Derek Hough as a Teddy Bear
Kelly Ripa and Ryan Seacrest as Game of Thrones characters
Trisha Yearwood as her husband, Garth Brooks
Sarah Michelle Gellar wrote, ''Am I unicorn? Am I mermaid? Am I part showgirl?!?''