Audrey Hepburn. Lauren Bacall. Diana Vreeland. And now, Sarah Jessica Parker (search). Tonight, she'll be crowned a "fashion icon" by Council of Fashion Designers of America (search) -- a rarely awarded honor that will be bestowed during the gala event known as the Fashion Oscars.

"Sarah Jessica has an innate sense of style and, in what she has chosen to wear on and off screen, has gone to extraordinary lengths to champion American fashion," says Peter Arnold, executive director of the CFDA.

"No matter what she wears," Arnold adds, sounding uncharacteristically star-struck, "you always notice her first."

SJP's style might seem effortlessly chic, but in both real and reel life, the actress devotes far more energy to pulling off those signature breezy and nonchalant looks than you might imagine.

Those who know her say Parker is incredibly finicky about everything she wears. She'll spend hours rooting through crates of shoes, agonizing until she finds the perfect pair.

Multiple fittings are required for formal gowns, and not just to ensure they kiss all the right curves.

She also makes a sport out of discovering up-and-coming designers and hunting down distinctive accessories.

Even something as innocuous as the selection of a T-shirt gets serious attention.

"She likes the little details, such as braided necklines and button twists," reveals Pam Protzel, the L.A. designer whose business exploded after Carrie wore one of her Ella Moss dresses on a date with David Duchovny on "Sex and the City." (search)

Parker, say those who know her, learned nearly everything she knows about fashion from "Sex and the City" costume mistress Patricia Field, the mad genius behind Carrie Bradshaw's look.

"Patricia basically gave her a crash course in fashion sensibility. She taught her how to dress, how to accessorize," says Lucy Sykes, fashion director at Marie Claire, referring to the touches -- including the nameplate necklace, the silk flower pin and the 4-inch Manolos -- that are now a style staple from Brooklyn to Beijing.

"Like Carrie, SJP makes a point of being a little wacky -- say, topping a classic suit with a bright red hat and accessorizing with pink shoes," Sykes says.

"But she knows that the unexpected, whimsical additions are exactly what will attract our eye."

It's that calculated whimsy that separates her from other actresses.

"Thanks to her non-conformist attitude, which she very much shares with Carrie, nobody will ever confuse SJP with anyone else," says Simon Doonan, creative director at Barneys.

"Great fashion is about experimentation and change -- it's not about the prissy, formulaic glamour that makes it so difficult to tell Scarlett Johansson and Charlize Theron apart."

Parker's seismic effect on the fashion world hit before the first season of the show wrapped.

"Her impact on all of us was to speed up and mix up the fashion cycle by wearing long one minute, short the next, followed by something unexpectedly radical," says Isaac Mizrahi, who'll be presenting her with her "fashion icon" award tonight.

"Despite the pace, she never makes a mistake. There's a sophistication to SJP that enables her to look as if she hasn't worked too hard which, of course, is part of her charm."

Her passion for fashion is simply infectious.

"You just know, by looking at her, how much fun she's having with the clothes," says Sally Singer, Vogue's fashion news director.

"You never feel she's thinking: 'Oh, shoot, I have to put on a gown.' Instead, she exudes this 'I am in New York City at this exciting event and I'm going to have fun.' Even when she goes casual -- as the downtown mom in her sailor pants -- or eccentric, you get a fantastic sense of delight that tempts the rest of us to try something new, which is precisely what a fashion icon should do: make us rethink the way we look, the way we shop, the way we present ourselves in public."

Most of us would wither under that level of scrutiny, but SJP seems to thrive in the attention.

"She has a fashion editor's eye and devotion to detail," raves Rob Haskell, fashion editor of W magazine. "Think of any one of the scenes when Carrie was standing on the street hailing a cab: The shoes were always perfect, the sweater always draped in an adorable way and the shoulders of her jacket were crisply tailored. This kind of precision doesn't happen by accident."

It's that rigorousness that separates her from the red-carpet pack.

"Unlike Halle Berry, Sarah Jessica never looks as if she's been stuffed into a really bad gown by a stylist," Haskell says.

"SJP is in control of a style vocabulary that spans black tie to slouchy, compared to someone like Nicole Kidman, who constantly trots out variations on the same strappy cocktail dress.

"At the other extreme, she has managed to avoid the self-consciously f-----d up craziness of Cameron Diaz."

Haskell sees a similarity between Parker and the Duchess of Windsor, Wallis Warfield Simpson, another unorthodox beauty who was renowned for her sense of style.

The Duchess, Haskell recalls, once said, "because she was nothing special to look at, her only option was to dress better than anyone else.

"I think there's an element of that to her look, which is that of a highly polished and savvy New Yorker. I don't think the Star will ever catch her in a state of dishabille in the supermarket."

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