1. It all started with Witherspoon and her inner circle.
"It was emails and friends telling friends, and everyone getting to each other through Reese," Allison Janney, who's nominated for Best Supporting Actress for her role in I, Tonya, told ET at the Palm Springs International Film Festival. "A lot of friends, and [Reese's] friends, told their friends. It was sort of a network of women who found out. So, yeah, it happened like that."
Witherspoon's Big Little Lies co-star, Laura Dern, echoed Janney's statements to ET during an interview with InStyle. "We were all having these side conversations about how to make a difference. Reese Witherspoon and I are very dear friends, so we were talking a lot about it," she shared. "It happened to be that a group of women were talking to each other, from actresses to agents to writers to producers. And suddenly we're rallying each other to say, 'How can we help all of us together to make a difference for friends across all industries?'"
The solution? The like-minded women said, "Let's get in a room," and planned everything out from there.
2. Witherspoon's been vocal about her own experiences with sexual assault.
At Elle's 24th Annual Women in Hollywood Celebration last October, Witherspoon heightened awareness, revealing onstage that she, too, was a victim of harassment. The incident happened when she was 16 years old.
"This has been a really hard week for women in Hollywood, for women all over the world, and a lot of situations and a lot of industries are forced to remember and relive a lot of ugly truths," she explained. "I have my own experiences that have come back to me very vividly and I find it really hard to sleep, hard to think, hard to communicate a lot of the feelings that I've been having about anxiety, honesty, the guilt for not speaking up earlier."
"[I feel] true disgust at the director who assaulted me when I was 16 years old and anger at the agents and the producers who made me feel that silence was a condition of my employment," she continued. "I wish that I could tell you that was an isolated incident in my career, but sadly it wasn't. I've had multiple experiences of harassment and sexual assault and I don't speak about them very often."
3. She's committed to making a real change in 2018.
While everyone was focusing on their personal goals for the new year, Witherspoon was dedicated to raising awareness for the issues that have long plagued Hollywood. Earlier this week, she took to Instagram to share with fans that there's no stopping her or her team of powerhouse pals this year.
"2018 let's do this," she captioned a motivational quote, which read, "It's on. Time to make the magic happen."
4. She's responsible for the accessory everyone will be wearing (and talking about) on Sunday.
In addition to wearing black in protest of sexual harassment and misconduct in Hollywood, many actors and actresses will be donning the official "Time's Up" pin. In a private meeting held last month at the Creative Artists Agency, Witherspoon asked Nocturnal Animals costume designer/stylist Arianne Phillips to create the pin that celebrities will wear on the Globes red carpet.
With the help of her jewelry designer friend, Michael Schmidt, Phillips told The Hollywood Reporter that she created the movement's logo and the pin design in just two weeks.
5. The actress is calling on women to stand together on the red carpet.
ET has learned that the blond beauty will be walking side by side with Longoria at the awards show. Expect to see their industry peers follow suit.
"This is a moment of solidarity, not a fashion moment," Longoria explained to The New York Times. "For years, we've sold these awards shows as women, with our gowns and colors and our beautiful faces and our glamour."
"This time the industry can't expect us to go up and twirl around," she added. "That's not what this moment is about."
6. Witherspoon and her "Time's Up" colleagues are hoping the movement will receive "widespread attention" for women in all industries.
"We also recognize our privilege and the fact that we have access to enormous platforms to amplify our voices," the letter of solidarity on timesupnow.com reads. "Both of which have drawn and driven widespread attention to the existence of this problem in our industry that farmworker women and countless individuals employed in other industries have not been afforded."
"To every women employed in agriculture who has had to fend off unwanted sexual advances from her boss, every housekeeper who has tried to escape an assaultive guest, every janitor trapped nightly in a building with a predatory supervisor, every waitress grabbed by a customer and expected to take it with a smile, every garment and factory worker forced to trade sexual acts for more shifts, every domestic worker or home health aide forcibly touched by a client, every immigrant woman silenced by the threat of her undocumented status being reported in retaliation for speaking up and to women in every industry who are subjected to indignities and offensive behavior that they are expected to tolerate in order to make a living: We stand with you," the letter continues. "We support you."
Hosted by Seth Meyers, the Golden Globes will broadcast live from The Beverly Hilton in Beverly Hills, California, on Sunday at 8 p.m. ET/5 p.m. PT on NBC. Hear more on "Time's Up," and everything we know about the awards show so far, in the video below.