All necessary to the plot lines, of course.
Amanda filmed steamy scenes for 2009's "Chloe" with both Julianne Moore and Liam Neeson. In her role as the title character, the "Mean Girls" star stripped down to play a call girl.
Olivia Wilde bared it all for 2006's "Alpha Dog." In the film, she played the girlfriend of the main character, Johnny Truelove (Emile Hirsch).
Patton takes full responsibility for taking off her top alongside Denzel Washington on their action comedy.
"It was my idea. It was something that I had thought about for a long time," Patton told Yahoo! Movies. "You know, you prepare for all these scenes ahead of time and I just thought, 'Gosh, it doesn't seem realistic for somebody who's been lovers with somebody for quite a while and they've just made love and now the conversation's happening that you would have a bra or a top on.' It just didn't make sense to me, so I thought the natural thing would be to not have one on."
The actress went from squeaky clean Jesse Spano from "Saved by the Bell" to sexy mama overnight after doing the movie "Showgirls" (1995).
Talk about redefining your image!
Check out which other stars let it all hang out for the cameras.
Earlier in her career Natalie denounced nude scenes, but in "Black Swan" she went all out for her lesbian nude scene, in a role that won her the Oscar. She explained at the time, "It's not raunchy, it's extreme."
It's rare for a male to go full on nude for a movie, but when comedy calls for it, Jason Segel is all for it.
In "Forgetting Sarah Marshall" (2008) Jason was overly comfortable in his birthday suit.
Paltrow had some steamy sex scenes in 1998's "Shakespeare in Love." She also won the Oscar.
Who could forget Harvey Keitel's performance in 1992's "Bad Leutenant"? A year later, he took it all off again for "The Piano."
Witherspoon played Susan Sarandon's daughter (who we'll get to in a bit) in 'Twilight' (1998) and went topless in one of the film's first scenes. It was the future Oscar winner's second big film, and one and only nude scene.
Viggo went full frontal in one of his first roles in 1991's "The Indian Runner."
Johnny Depp's new girlfriend took it all of for a steamy threesome scene in the 2008 dud 'The Informers.'
The 'Kill Bill' star dropped her top onscreen when she was just 18 in a scene with John Malkovich in the film 'Dangerous Liaisons.'
The film ended up winning three Oscars.
The actress first took it all off for the movie "Mildred Pierce." Co-star Kate Winslet, who is naked in almost every movie she's in, was there to provide encouragement.
"I looked at Kate and she was like, 'You've got to do it. Trust me, it's so brave. Put a merkin on and you'll be fine,'" Wood said.
A merkin is a toupe for one's, well, yeah.
Before she was woo-ing Don Draper on "Mad Men," Jessica took it off for a steamy scene in "Hot Tub Time Machine" in 2010.
This film won zero Oscars. But it was funny.
Mischa first stripped off her clothes for "The Oh in Ohio" in 2006 and did it again a year later for "Closing the Ring." According to Mischa, that won't be the last time she bares all for the camera.
"I don’t mind nudity as long as it’s necessary to the story," Mischa has said. "I mean it’s a bit weird because you’re, like, naked in a room full of strangers."
Susan Sarandon has seemed like a mature star for decades, but when she first got her start, back in 1970, her first role called for her to lie naked in a bathtub in "Joe." She has since done a few topless scenes for movies like "Pretty Baby" and "The Hunger" and "Atlantic City."
The Downton Abbey star said she was “naive” when she agreed to go topless in the 2011 film "Albatross" and would not have done it had she known she could have said no.
After being hugely successful in the '80s with movies like "The Breakfast Club" and "Sixteen Candles," Molly's career went a bit stale. She tried to vamp it up with a sexy role in "Malicious" in which she went topless in 1995, but that didn't quite help.
Screen shots of Kristen Stewart topless in the film "On the Road" leaked ahead of the movie's release.
"I wanted to do it," she said of filming the risque role. "I love pushing," she said earlier this year while promoting the film. "I love scaring myself."
"The Hangover" was outrageously funny and had many "wow" moments. One that stands out is when Ken Jeong (center) jumped out of a trunk naked. At least by the second movie, shown here, he was allowed to wear clothes.
Check out which other stars shocked audiences by going nude.
The actress displayed her flawless body in 1996's "Striptease." She later went topless again in a very different role for "G.I. Jane" a year later.
The former teen heart throb is all grown up and going to make ladies swoon in his upcoming flick "Paperboy."
"As much as I love everything I've done, this is a new frontier for me," he said at the press conference for his movie that premiered in Cannes in May. "It's incredibly fulfilling. It's a dream. Hopefully, I can keep doing things like this," he continued.
So just what kind of nudity is there? "He was in his underwear half the time," said singer Macy Gray, who narrates the movie.
Sandra Bullock's flick "The Proposal," marked the first time the actress stripped down on-set.
"Sadly, my first and last nude scene got laughs, so I had to be very secure with that," she said. "It was all about choreography. I mean, literally when you read it on the page, you saw it, and then you realized, 'OK, there is no way to shoot this unless you are buck naked!' Then I went, 'Go to the gym, cut out the carbs!'"
The former Mrs. Tom Cruise did her first nude scene for the 2000 film "The Gift" for "Spider Man" director Sam Raimi.
Ryan was naked a lot in "Crazy, Stupid, Love." On the left, he stands over co-star Steve Carell and gives him an eyeful.
''Was it awkward? No, actually I kind of enjoyed it," admits Steve. "He's a very handsome guy, you know, there's no disputing that. And I am not ashamed to say that I find him very attractive."
Anne Hathaway shed her Disney image by appearing in several nude and sex scene in the film "Havoc," which was not released in U.S. theaters due to godawful reviews. Anne first appeared topless in America (onscreen that is) in the film "Brokeback Mountain."
Kate Winslet first revealed her assets in the mega-hit "Titanic," then proceeded to do it again and again and again and...
Diane Keaton, who is usually covered head to toe, was partially nude in the raunchy 1969 hit "Looking for Mr. Goodbar," but did the "Full Monty" for the the first time at the age of 57 in the 2003 film "Something's Gotta Give." Apparently, the movie title was talking about her clothes.
Many were introduced to Hayek in Robert Rodriguez's "Desperado."
All of her.
Denise Richards had some memorable lesbian nude scenes in the 1998 film "Wild Things." Gee, wonder what caught future husband Charlie Sheen's eye?
Rosario Dawson went completely nude in the 2004 Oliver Stone movie "Alexander." Good thing, too, because she was the only reason Will Smith got through their love scene in "7 Pounds." Dawson told New York Magazine "it was funny and actually very precious to see how nervous and shy Will was about it. Before we went in for our kiss, he was literally psyching himself up, like, "Yo, we're gonna kill this scene!" I'm like, "Uh, yeah, Will, I brushed my teeth today, we're all good."
Meg Ryan made her nude debut in the 2003 flick "In the Cut," as did co-star Mark Ruffalo.
Angelina Jolie appeared semi-topless in "Hackers" in 1995 then went the fully nude route in the film "Gia" in 1998, romping through several lesbian love scenes along the way.
Halle Berry went topless in the 2001 film "Swordfish" before getting naked again that same year for her Oscar-winning performance in "Monster's Ball."