Which Celebs Have Accepted the #4PercentChallenge — and What Does It Mean?

At this year's Sundance Film Festival, Tessa Thompson posed a challenge to a room full of film industry players: commit to working with a female director in the next 18 months. The call came just a few weeks after Regina King used her winning speech at the Golden Globes to implore the audience to work with 50 percent women on their projects.

Thompson partnered with Time's Up and Dr. Stacy Smith of the Annenberg Inclusion Initiative on the announcement, which Smith is calling "the 4% challenge." Why four percent? That's the measly number of studio films in the last decade that have been directed by a woman.

Since Time's Up issued its call to action, Hollywood players have responded in heartening droves. Ahead, see some of the big names to join forces with the challenge so far. Then, check out the full (and growing) list of actors, writers, producers, directors, and studio heads who have accepted the #4PercentChallenge on the Time's Up website.