Here's a look at some of the top costumes.
"Riverdale" stars Camila Mendes and Lili Reinhart dressed up as their favorite "Napoleon Dynamite" characters. No word if they carried Tater Tots in their pockets.
George Clooney, Cindy Crawford and Rande Gerber donned flight outfits for their Casamigos party.
John Legend couldn't have been a more amazing dad taking his little princess Luna out for the occasion.
Sarah Hyland and her boyfriend went dressed up as "Taco Belle," a funny take on the fairy tale classic.
Kendall Jenner was channeling her inner "Austin Powers" for the holiday.
Harry Styles needed no introduction, as he was the legendary Elton John.
Ryan Seacrest went as fashion icon Karl Lagerfeld.
Actress Gabrielle Union went as another celebrity, Gwen Stefani.
And last but certainly not least, Joe Jonas dressed up as his fiancee Sophie Turner's "Game of Thrones" character. Epic!