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InStyle's editorial guidelines Updated on March 27, 2015 @ 11:59AM Pin Share Tweet Email Photo: Jon Kopaloff/FilmMagic Looks of the Week 01 of 22 Camilla Belle David Buchan/Getty Images for Westfield Camilla Belle stepped out to lend her support for the St. Jude Holiday Campaign for Westfield at Westfield Century City in ladylike full midi skirt with a sheer black eyelet overlay, both by Shoshanna, that she styled with a matching top, a long black beaded necklace, and sweet pink metallic bow-accented sling-backs. 02 of 22 Sienna Miller David M. Benett/Getty Images for Rolls-Royce Motor Cars Sienna Miller graced a Rolls-Royce preview in an elegant floral-strewn blouse that she tucked into a breezy pair of matching wide-leg pants, styling them with delicate jewelry, a metallic minaudiere, and red velvet pumps. 03 of 22 Lily Collins Donato Sardella/Getty Images for Elie Saab Lily Collins, likewise, selected a one-piece for the private Elie Saab-hosted dinner. Instead of a jumpsuit, she stunned in a black long-sleeve Elie Saab romper with a lace sleeve and a black thin leather belt. A black Elie Saab handbag, EF Collection jewelry, and edgy mesh Louboutin pumps. 04 of 22 Jennifer Aniston Tim P. Whitby/Getty Images Jennifer Aniston, whose sartorial track record consists mostly of LBDs, changed things up for the London premiere of Horrible Bosses 2-she added a dash of color with a sexy one-shoulder Antonio Berardi LBD that revealed a glimpse of a red-hot corset underneath. Long Jennifer Meyer earrings, an Irene Neuwirth cuff, and black patent Louboutins completed her look. 05 of 22 Reese Witherspoon Jesse Grant/Getty Images for Leisure Opportunities Reese Witherspoon stunned at the Latin American premiere of Wild at the Los Cabos Film Festival in a white-and-navy twill laser-print sleeveless Calvin Klein Collection dress that she simply styled with an EF Collection ring and optic white Casadei pumps. 06 of 22 Olivia Wilde Mike Marsland/WireImage Olivia Wilde sizzled at the world premiere of Horrible Bosses 2 in a black cut-out Michael Kors column, complete with a black python Michael Kors clutch and black Stuart Weitzman sandals. 07 of 22 Rose Byrne Lisa Maree Williams/Getty Images As the new face of Oroton, Rose Byrne stepped out for the event that was thrown in her honor, selecting a little white sheath dress with a pearl-studded statement necklace, a metallic Oroton clutch, and neutral peep-toes, for the occasion. 08 of 22 Rooney Mara JP Yim/Getty Images Rooney Mara joined in on Maison Cartier's 100th anniversary celebration of La Panthere De Cartier in a sexy-sweet Givenchy LBD with peek-a-boo lace panels and a satin hem. Her trademark vampy lip and black Stuart Weitzman sandals rounded out her ensemble. 09 of 22 Taylor Swift Raymond Hall/GC Images Taylor Swift promoted her hit album 1989 on Good Morning America in a black jacquard knit long-sleeve crop top and a matching knee-length pencil skirt by Calvin Klein Collection, complete with radish-red suede Stuart Weitzman pumps. 10 of 22 Hailee Steinfeld Michael Tran/FilmMagic Hailee Steinfeld pulled out all the stops for The Homesman screening at the AFI Fest 2014, selecting a strapless purple tea-length Monique Lhuillier design with a full floral skirt and styling it with a Jennifer Fisher ring and asymmetric strappy sandals. 11 of 22 Katie Holmes Max Lakner/BFAnyc/Sipa USA Katie Holmes joined the Marchesa founders for a midnight supper (a St. Regis tradition) in celebration of their appointment as St. Regis Connoisseurs in a full embroidered black lace Marchesa cocktail dress, with a red clutch and black pumps. 12 of 22 Camilla Belle Donato Sardella/Getty Images for Vogue To celebrate Tory Burch's new watch collection, Camilla Belle stepped out in head-to-toe Tory Burch, which included a colorful striped pullover and a matching silk skirt with a cherry-red mini chain clutch, bow-topped pumps, and (of course) a Tory Burch timepiece. 13 of 22 Lupita Nyong'o Dimitrios Kambouris/Getty Lupita Nyong'o sported high-fashion bike shorts on the red carpet, selecting ivory Chanel Couture separates that boasted a regal high-neck neoprene tunic dress and matching shorts with exquisite gold beadwork, complete with gold Kurt Geiger pumps. 14 of 22 Jennifer Lawrence Dave J Hogan/Getty Jennifer Lawrence wowed at The Hunger Games: Mockingjay Part 1 after-party in a risqué plunging white Mugler by David Koma halter column with a spliced accent and a thigh-high slit. Black diamond Norman Silverman studs and silver ankle-strap sandals completed her look. 15 of 22 Elizabeth Banks David M. Benett/WireImage Elizabeth Banks shimmered at The Hunger Games: Mockingjay Part 1 after-party in a liquid rose gold strapless Monique Lhuillier design, piling up on the metallic with a matching skinny belt, a rose gold Lee Savage clutch, gold Jennifer Fisher jewelry, and rose gold Paul Andrew stilettos. 16 of 22 Keira Knightley Jon Kopaloff/FilmMagic Keira Knightley hit The Imitation Game screening in a stunning stone embellished Chanel Couture LWD (foregoing its matching biker shorts), with nude pumps. 17 of 22 Julianne Moore Dave J Hogan/Getty Julianne Moore slipped on an extraordinary LBD-a ruched Balenciaga design with beaded off-shoulder detailing, latticework at the shoulders, and sheer sleves-for the London premiere of The Hunger Games: Mockingjay Part 1. Classic black sandals and a slicked-back low pony completed her look. 18 of 22 Jennifer Aniston Jon Kopaloff/FilmMagic Jennifer Aniston dialed up the heat at the Motion Picture Academy's 6th Annual Governors Awards in a black beaded floral-embroidered Zuhair Murad slip dress that she impeccably styled with drop Irene Neuwirth earrings, a Melissa Kaye Jewelry bracelet, a black clutch, and patent black pumps. 19 of 22 Jessica Alba Jason LaVeris/FilmMagic Jessica Alba was the picture of perfection at the 2014 Baby2Baby Gala in a breathtaking strapless Andrew Gn creation with a gold leaf bodice and a frothy white tulle skirt, picking up on the metallic accents with vintage earrings, a Tiffany & Co. ring, and a bronze Brian Atwood clutch. 20 of 22 Kate Hudson Stefanie Keenan/Getty Images for Baby2Baby Kate Hudson was honored at the 2014 Baby2Baby Gala, selecting a plunging raspberry cut-out Stella McCartney column for the occasion. Tiffany & Co. jewelry and a black sparkly Jimmy Choo clutch completed her look. 21 of 22 Michelle Monaghan Jon Kopaloff/FilmMagic Michelle Monaghan stunned at the 2014 Governors Awards in a sweeping pink-aqua-white color-blocked J. Mendel number with a sexy thigh-high slit, adding bling with a gold Irene Neuwirth bracelet and a metallic clutch. 22 of 22 Emily Blunt Jon Kopaloff/FilmMagic Emily Blunt was striking at the 2014 Governors Awards in a beautiful geranium floral-embroidered Michael Kors gown, complete with Dana Rebecca Designs jewelry, and an emerald Rauwolf clutch.