Lady Gaga, Justin Bieber and Amelia Earhart all stopped by "Today" this morning ... or at least people dressed as them did!

Meredith Vieira, Natalie Morales, Ann Curry, Al Roker and Tamron Hall all dressed up in some pretty convincing costumes for this year's Hallowen episode -- which Tina Fey and Will Ferrell also appeared on.

Check out all the crazy costumes -- and let us know what you wore to work today!