Fashion Looks of the Week By InStyle Editors InStyle Editors Facebook Instagram Twitter Our editors and writers comprise decades of expertise across the beauty, fashion, lifestyle and wellness spaces in print and digital. We prioritize journalistic integrity, factual accuracy, and also having fun with every story we share. InStyle's editorial guidelines Updated on March 27, 2015 @ 11:59AM Pin Share Tweet Email Trending Videos 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.