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Twin Set
Off duty, Rachel Bilson, 24, and Mischa Barton, 19 (far right), have started mirroring each other's style sensibilities from top (long, straight hair and long necklaces) to bottom (shorts with peep-toe heels). Dressing to go to work, Bilson says, "is like going back to school: You plan out your outfit the night before, even though you know you have wardrobe."

School Ties
What did they do this summer? Bilson shot the movie The Last Kiss, while Barton filmed the period drama Decameron in Italy. They've been back on The O.C.'s set since July (the show returns Sept. 8). "I was so excited when we got back; it was like a big reunion," says Barton. Adds Bilson: "It's hard to say it's work. You have a good time with your friends."

Good Buy Girls
The trendy twosome are regulars at Hillary Rush in L.A. "They both have a great eye," says boutique owner Hillary Rush. "And sometimes they buy the same thing." Often skimming the racks with them is Barton's other constant companion, her 17-year-old sister Hania (center).

Fan Fare
When Bilson's beau, Adam Brody, performed with his indie rock band Big Japan at L.A. clubs in July, Bilson played the role of No. 1 fan—and brought Barton along.

Puppy Love
Last year Bilson and her on-and offscreen boyfriend, Adam Brody, adopted a pit-bull terrier, Penny Lane, from a rescue center. This summer Barton followed suit, taking home an abandoned mixed-breed dog named Charlie.

I'll Be There For You
Back at work not long after her breakup with oil heir Brandon Davis, Barton "was in a great mood," says O.C. creator Josh Schwartz. "You would never know. It doesn't come up." For her part Bilson helped Barton bounce back with regular girls' nights out together—from dining in Beverly Hills to hitting Hollywood hot spots like Mood and attending a party honoring Bilson (above)—all of which seemed to do the trick. When recently asked about how she's faring, Barton replied, "Everything's been really good."