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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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Fashion’s two favorite pixies, Ashley Olsen and Mary Kate Olsen, made a spirited appearance at the Chanel fall 2008 ready-to-wear fashion show in Paris. The fashion-loving twin sisters wore matching oval-shaped sunglasses to the show. Sunglasses inside: chic or shady? Discuss!

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Rumored lovebirds Lance Armstrong and Ashley Olsen walked the red-carpet—separately—at the grand re-opening celebration of The New Museum On The Bowery in New York City. On the other hand, conflicting reports have surfaced that Ashley was cozying up to Josh Lucas at the same event. Lance or Josh: Who do you think should be Ashley’s new beau?

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Mary-Kate Olsen, Amy Winehouse and Ashley Olsen attended the launch dinner of The Row hosted by designers and mini moguls, Mary-Kate and Ashley Olsen, at Harvey Nichols in London. Do you think an Olsen/ Winehouse collaboration is in the works?

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The queen bee of chic Ashley Olsen attended the Calvin Klein Collection spring 2008 fashion show in a loose white t-shirt and black high-waisted skirt. Kudos to Olsen for choice so-of-the-moment accessories: grey ankle booties, large triple buckle belt, and men’s watch.

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James Blunt and the always fashionable Mary-Kate Olsen and Ashley Olsen attended the Hampton Social @ Ross Concert by James Taylor in East Hampton, New York. Onlookers say Mr. Blunt took a keen interest in Mary-Kate but his advances were resisted.

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Ashley Olsen wore her favorite crocodile Fendi bag out while waking with her bodyguard in the West Village, New York City. Ashely, and her sister Mary-Kate, are in town for a photo shoot for their new clothing line, The Row.

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Mary-Kate and Ashley Olsen are fashion chameleons constantly being photographed for magazines in search of the next big trend. Photographers have always had trouble identifying which twins was which but it seems like the girls haves traded looks identified with them for most of 2006. Mary-Kate was known as the honey-blonde-boho-babe with loads of extensions, Ashley, the blonde vamp, but sisterly envy took over and the two have traded places with MK sporting a bleach-blonde goth vibe and Ashley displaying brown tones more in tune with her natural hair color (almost a match to stunning full-brows). In any event, the girls are constantly fascinating and we can wait to see what their next look will be!