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Actress Mary Kate Olsen arrives at the Metropolitan Museum of Art Costume Institute Gala, Superheroes: Fashion and Fantasy, held at the Metropolitan Museum of art on May 5th, 2008 in New York City. Mary Kate dons gold sequins, looking reminiscent of Shirley Eaton’s gold body paint in the James Bond film ‘Goldfinger’. With the success of Mary Kate and Ashley Olsen’s recently launched fashion lines, one could say everything this mini-mogul touches turns to gold.

Hilary Duff seems to have taken her inspiration not from a Superhero, but rather from the city that has provided a backdrop and home to so many. Duff’s beaded silver dress with Art Deco detailing conjures images of one of Gotham’s most famous buildings, the Chrysler Building.

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Hilton…Simpson…Olsen…Spears…Duff…Kardashian…. Famous sisters are the best (and the worst). Celebrity siblings are all over the place right now, but we have always been interested in famous women who come in pairs. The Gabor sisters, The Landers sisters, Joan and Jackie Collins were duos previous generations kept tabs on.

Sisters are fun to watch: When sisters begin to share the spotlight sometimes they try to differentiate themselves from one another by establishing defining looks, such as Mary Kate and Ashley Olsen (dark boho vs sunny blond) or Jessica and Ashlee Simpson (sunny blond vs edgy rocker). We can witness them ease into their roles and equalize aesthetically (Olsens/ Simpsons).

Sisters are sexy: When sisters’ looks and attitudes diverge wildly, the game of:“which sister would you rather____?”is likely to ensue. When their looks converge, the pairing still provides fuel for fantasies.

Sisters are us: When one sister falters we can shift our hopes to the other one. When one seems appears to be the underdog, we can root for her.

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Though it is fascinating to watch sisters who are both in the public eye, it is refreshing to see a celebrity with her “normal” sister. Antonia Kidman is primarily a journalist, but glided into the public eye by accompanying Nicole to parties, premieres and shopping. Mia Farrow is the most widely known daughter of Maureen Sullivan, yet she has siblings with fantastic bone structure who remained somewhat unknown despite brushes with acting.  One of Mia’s sisters was the inspiration for the Beatles’ Dear Prudence.  Whatever a lesser known sister is up to, they offer a different perspective on her famous sibling. The citizen sister grounds her celebrity sister more than many interviews or magazine pieces can.

View this lightbox to see the full gamut of our favorite sisters.

Pictured: Peaches and Trixie Gelof vs. Catherine Deneuve and Françoise Dorléac, Lindsay Lohan and Ali Lohan vs. Maria Scicolone and Sophia Loren, Lisa Roberts Gilliam and Julia Roberts vs. Cameron Diaz and Chimene Diaz

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The young, fabulous, and beautiful came out to support a wonderful cause, PS Arts, a non-profit organization dedicated to restoring arts education in public schools at the Chanel store in Beverly Hills. Among the many attendees at the party, Hilary Duff was the clear fashion winner looking fun and fresh in a Chanel mini skirt and beret. Karl would have been proud!

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Never one to commit a fashion faux pas, host Hilary duff hit all the right notes in her Corey Lynn Carter mini dress at the 2007 Teen Choice Awards in Universal City, California. Debuting her new honey colored locks—that matched her embellished ensemble perfectly—Duff, is the only person to host The Teen Choice Awards twice in its nine-year history.

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Hilary Duff posed with some new friends at the International Polo Club’s annual Polo Ball black-tie gala in Wellington, Florida. Duff was a guest of John Goodman, co-founder of International Polo Club, Palm Beach. Where was Haylie?