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InStyle's editorial guidelines Updated on March 24, 2015 @ 01:27PM Pin Share Tweet Email Photo: Frazer Harrison/Getty Images 20 Best dresses 01 of 20 Gwyneth Paltrow in Stella McCartney, 2008 Dimitrios Kambouris/WireImage "Paltrow gives the illusion of giving something away, while still having a kind of ladylike reserve," says InStyle fashion director Hal Rubenstein. "This sexy mini, by pal Stella McCartney, plays up her best assets and shows off her killer body." 02 of 20 Julia Roberts in Valentino, 2001 BEImages "Instead of using a stylist to pick a gown for her Oscar-winning night, Roberts turned to her niece, Emma. This Valentino number gave a huge boost to vintage," says InStyle fashion director Hal Rubenstein. 03 of 20 Kate Moss in Dior, 2005 Erik C Pendzich/Rex USA "On the one hand this Dior couture dress is lingerie-inspired and sexy, yet the shape is quite simple. Finishing off the look with tousled bed-head proves that Moss's instincts are always right," InStyle fashion director Hal Rubenstein says. 04 of 20 Jennifer Aniston in Burberry Prorsum, 2009 Frederick M. Brown/Getty Images "I love the idea of androgyny," says InStyle fashion director Hal Rubenstein. "And if you're going to do menswear, you have to sex it up. Aniston really played against type in this Burberry Prorsum pantsuit." 05 of 20 Beyoncé in Elie Saab, 2009 David Fisher/Rex USA "This Elie Saab dress is perfect for her—it celebrates everything and hides nothing. She understands what works for her body," says InStyle fashion director Hal Rubenstein. 06 of 20 In Christian Dior, 2010 Frazer Harrison/Getty Images At the Golden Globe Awards, the high slit in Cotillard's teal gown revealed a panel of lace detailing. 07 of 20 Penelope Cruz in Atelier Versace, 2007 Gilbert Flores/CelebrityPhoto.com "The beautiful pink color of this Atelier Versace gown perfectly accents Cruz's skin, while the silhouette manages to be both sleek and romantic at the same time," says InStyle fashion director Hal Rubenstein. 08 of 20 Natalie Portman in Givenchy Baverel-Garcia/Starface/Retna Ltd. "Portman doesn't look like most young stars," says InStyle fashion director Hal Rubenstein. "She likes to play with volume and proportion. Here, she takes a wild Haute Couture look by Riccardo Tisci for Givenchy and pairs it with perfectly polished hair and makeup." 09 of 20 Nicole Kidman in Yves Saint Laurent, 2003 SGranitz/WireImage.com "Kidman has a fearless approach to fashion. The lavender color of this YSL gown offsets her red hair, while the silhouette is a nice play on proportion," says InStyle fashion director Hal Rubenstein. 10 of 20 Anne Hathaway in Giorgio Armani Privé, 2009 Fernando Allende/Broadimage "This Armani Prive dress has huge wow factor, says InStyle fashion director Hal Rubenstein. "What's cool is that the iridescent pailettes lengthen her body and accent her curves. It's one thing to have a good body, another to be proud of it!" 11 of 20 Cate Blanchette in Valentino, 2005 Stewart Cook/Rex USA "When Valentino approached her to wear one of his dresses to the Oscars the year she was nominated for The Aviator, Blanchett said yes, as long as she was the only one to wear Valentino. She doesn't dress like anyone else," says InStyle fashion director Hal Rubenstein. 12 of 20 Jessica Alba in Marchesa, 2008 Axelle Woussen/Bauer-Griffin "Six months pregnant at the time, Alba looks radiant in this Marchesa stunner. The jewel tone allows her to positively glow," says InStyle fashion director Hal Rubenstein. 13 of 20 Leighton Meester in Bottega Veneta, 2009 Jen Lowery/Startraks "Meester is anything but conventional. She is having a blast with fashion, and this Bottega Veneta dress is no exception," says InStyle fashion director Hal Rubenstein. "The fluidity of this goddess gown is pure glamour. " 14 of 20 Eva Mendes in Dior, 2009 Janet Gough/CelebrityPhoto "In the midst of an economic crisis, this fearless Dior dress brought everyone's spirits up. Mendes knows how to dress for her body and simply has fun with fashion," says InStyle fashion director Hal Rubenstein. 15 of 20 Rachel McAdams in Emanuel Ungaro, 2009 Ethan Miller/Getty Images "There's something very old Hollywood glamour about her look," says InStyle fashion director Hal Rubenstein. "This Emanuel Ungaro mini brings her back to that romantic place, while still looking modern." 16 of 20 Megan Fox in Roberto Cavalli, 2009 Rex USA "After Fox wore this barely-there number to a premiere, every last red Cavalli dress sold out in three days. Everyone was talking about the way she looked," says InStyle fashion director Hal Rubenstein. 17 of 20 Keira Knightley in Vera Wang, 2006 Dan MacMedan/WireImage "The rich burgundy color of this Vera Wang gown is unbelievable," says InStyle fashion director Hal Rubenstein. "Knightley has a great sense for color, and always chooses tones that get her noticed. She dresses with a French sensibility even though she's British." 18 of 20 Jennifer Connelly in Balenciaga, 2007 Dimitrios Kambouris/WireImage "The metallic shine of this Balenciaga dress works well with her pale skin tone. The short silhouette and hair worn down keep the look young and modern," says InStyle fashion director Hal Rubenstein. 19 of 20 Carey Mulligan in Vionnet, 2010 Nick Sadler/Startraks InStyle fashion director Hal Rubenstein says, "Mulligan doesn't run to the safety of a solid for the red carpet. The print of this Vionnet gown is romantic, while the shape is modern. She's got a level of awareness and quirkiness that sets her apart from other actresses." 20 of 20 Kate Beckinsale in Calvin Klein, 2009 Frazer Harrison/Getty Images "The bias cut of this J. Mendel gown shows off Beckinsale's curves. She always incorporates one element to make the look a standout, and far from minimal," says InStyle fashion director Hal Rubenstein.