At the West Twenty-second Street headquarters of Dualstar, where The Row is based, the sisters sit at a swatch-strewn studio table. Ashley is bundled up in a pilled Marc Jacobs oatmeal sweater pulled over an old black Moschino slipdress and a rusty-red shahtoosh looped around her neck. Mary-Kate had tramped through the January snow in an oversize ribbed-leather motorcycle jacket and multiple black layers, a neon Guatemalan knitted hat perched on her head. It is a jolt how far down you have to look at them, not to mention how many clothes they like to wear between them.

The girls laugh about their lack of stature. Even their 22-year-old little sister, breakout actress Elizabeth Olsen, whom they can’t wait to dress for Cannes, is taller than they are. “We had to share the height!” jokes Mary-Kate. All their lives, they say, they’ve watched and respected women bigger than themselves. “We grew up with adults, surrounded by a lot of women who had great style,” she continues. One of them is Jill Collage, the twins’ former on-set guardian, a tall, slim woman in a black pantsuit from The Row, who is roaming the office. The twins appointed Collage president of Dualstar in January 2010 to oversee all departments and planning. “We made sure they were surrounded by women who were truly nurturing,” Collage says, “their acting coach, their teachers, their stylist—so they didn’t feel the pressure.”

The pre-fall collection is just in. Ashley holds out a plain man-tailored sand-colored overcoat, saying, “Try this. It’s cashmere and ermine.” Putting it on is almost a physical shock of pleasure. The cut is subtle, exact, formal yet easy, and looks perfect proportionally. Ashley founded The Row in 2006 in her drive to make a luxurious basic white T-shirt to suit many women—she meticulously tested it on all shapes and ages, 20 to 60, trying to find a commonality of fit and attitude. Still, the Olsens were up against a cynical audience of retailers; suspicious given the bad reputation attached to celebrity lines, nobody really believed the girls were designing it at first. “We hired a showroom and talked buyers through,” remembers Ashley. “People would drill us about fabric, where we’d make it,” says Mary-Kate. “The first season, customers bought it, so the stores came back. And drilled us again.”

The point was, they were aiming at the very people who are likely to shun celeb-related collections—picky women of the world who buy clothes only on intrinsic merit. That’s why they called it The Row—an anonymous name loosely derived from Savile Row, the home of British tailoring. Since then, while no one has particularly been watching (except the stores that can’t keep their neat jackets with flattering wrist-length sleeves, or great white blouses and well-cut pants, in stock), the collection has grown, rapidly filling a gap for American-everywoman daywear that few, if any, other young designers have attempted to approach. “It’s classicist, no-bother stuff. I live in it,” says Lauren Hutton, who became a friend after modeling for the label’s look book. “It’s beautifully tailored in a modern way. It just fits, chicly. You know, I look up to them.” They’ve steadily lavished attention on the way clothes feel, and the more they’ve refined the quality, the better it has sold. Now they’re at the point where The Row employs one extra designer, an assistant, and a bag designer: It’s tight and efficiently run. If The Row offers upper-echelon-designer prices (it does—and they’re rising, what with the addition of fur and precious skins), what sets it apart is the young American pragmatism. Ashley is obsessed with things’ being versatile and multi-optional for many women. “Each of the looks we’ve shown for fall was designed top to toe, but then we thought about how everything should dismantle as separates.”

Still, how have they pulled any of this off without a formal design education? “Fair question,” replies Ashley, “but Dualstar started when we were six. And we had a collection with Walmart at twelve, which was the upper tier of the tween market. It was before celebrity designers.” “And we were really designing it,” adds Mary-Kate. “It would be jeans, a bit bohemian, or with a little blazer. It was really fashion-forward.”

The girls took control of the company built on their childhood earnings in TV and movies on their eighteenth birthday, when they bought out the former owners, took a hiatus from acting, and moved to New York. Dualstar has now had retail sales of $1 billion. What could possibly have qualified them for such corporate responsibility, or made them even want it?

Mary-Kate, expert thrower of the stunning conversation stopper, replies, “Well, at that point we had been working eighteen years.”

As blonde and cute and as endlessly measured in paparazzi pictures and gossip-column inches as the Olsens are, you quickly learn how stupid it is to think of them as dinky little celebrity girls with an accidental business in clothes. Today, Dualstar, which owns their back catalog of movies and TV shows, also operates a sizable fashion business strategically layered to catch all levels of the market: The Row at the luxury end, Elizabeth and James as the bigger contemporary slice, and Olsenboye, accessibly priced for teens, which reaches the mass market in partnership with JCPenney.

The twins had been brought in on all business and production decision-making since childhood, vouches Collage. Ashley thrived on absorbing business knowledge. “I loved being in those meetings!” she declares. “We were working with the smartest people, learning from them.” If Malcolm Gladwell is correct about the way children who put in 10,000 hours of specialist study become outliers in later life, then the knowledge she absorbed virtually qualified her for an MBA before the age of sixteen.

Ashley is often considered the financial brain, Mary-Kate the creative—though it’s more complex than that. Sometimes—you see it in photographs, where they stand, shoulders touching, half-turning inward to each other—they almost seem like a single, self-protecting organism. “Some of our memories are shared,” Mary-Kate says at one point. “We don’t know what actually happened to whom. One of us was stung by a bee, but we can’t remember who, because we both felt it.”

This twinny-creative dynamic was evident during a fall design meeting weeks earlier. Their fabric-sourcer had brought in an array of luxurious samples of leathers, skins, and fur, which they set about stroking and distinguishing between. “See, all we do is pet things all day!” joked Mary-Kate. Ashley pulled out a length of glossy, chocolate-colored python. “I want to make driving gloves out of these, with the knuckles out!” She got excited over how they’d sourced a specialist Los Angeles glove-maker, Gaspar, which has a history dating back to nineteenth-century Europe. They care about tradition and provenance, producing locally as much as they can to support employment, but then they’ll fuse it with pure twenty-first-century girl-think: Some of the gloves have fingertips made in high-tech treated leather so you don’t have to take them off when using a touchscreen.

On another desk were the makings of their next brand extension: bags. “I’m obsessed with branding,” said Ashley, turning a narrow rectangular brass snap over to show the tiny logo concealed on its edge—a finishing component for their supremely supple, superdeluxe range of crocodile and snakeskin backpacks, computer bags, and clutches. One design, which ranges from mini–shoulder bags to totes, has two compartments sandwiched together, with textured skin on one side, suede on the other. It’s called the Twin.

Ashley picked up a length of leopard-print goatskin. “That would make a great coat,” she mused. Without any cue, Mary-Kate stood up and turned her back, while Ashley draped it on her. A split second later, Mary-Kate was spontaneously shimmying it up and bunching it into a hat. During New York Fashion Week, the result: The goat leopard is the showstopper opener of their fall presentation, and the hat has become the biggest fox snowboarder beanie ever, pushed to the limit of witty, casual chic.

Of the two, Ashley—“Smashley,” as her twin sometimes calls her—was clearly keener to leave acting behind. “I am so proud of what we did. We made kids smile every day. But we had done the most we could do.” Wasn’t it frightening to stop? “There was a fear,” admits Mary-Kate, catching her breath and sighing, “but also, an exhale.”

Escaping a life of being hounded in L.A. was also a major relief. “The press here in New York respect you more,” Ashley notes. “It was the worst in Los Angeles when we got our license. They would follow us. They knew where we lived. And you don’t know who these people are. People just out of jail.” Being young and stalked has taken its toll. “We are paranoid,” Mary-Kate states, glancing out the window. But isn’t that not paranoia, because what you’re imagining is what’s happening? “Well,” she responds, “we have no way to tell the difference.”

As saddening and damaging as the consequences of childhood stardom could have been (and, as publicly documented, the burden fell more on Mary-Kate), there is no shadow over the part of their childhood careers that involved clothes. What they went through to fit their tiny frames has a direct connection to their adult work as design directors: They know how cut works, intimately. The wardrobe departments of Two of a Kind and So Little Time were effectively their tailoring and dressmaking school, three days a week from age nine months to eighteen.

“It was so fun because it was all about clothing and hairstyles,” Mary-Kate recalls. “We had to change twelve times every episode. There would be five or six racks of clothes there, and they cut them down to fit us—even Chanel.” “We were involved 100 percent in the fittings,” says Ashley. “And at that age when you become so crazy about how you look,” adds Mary-Kate, “sometimes there were three or four fittings. All our memories are of shooting.”

With all that dressing up, did they still want to play with clothes at home, like other girls? “Totally!” shouts Ashley. “I’d go through my closet all the time, putting things together—it looked like a tornado hit it.” “Still does,” they chorus, then play-bicker over a Céline sweater Mary-Kate had hijacked from Ashley. So there’s a demarcation line between their wardrobes? “Hmm,” says Smashley. “There’s hers, there’s mine. And a huge ‘maybe’ pile.”

That pile contains some amazing stuff: They’d added to it just that week, when Ashley had put in an order for Balenciaga pre-fall, and Mary-Kate had scored a “kind of Mick Jagger” Chanel couture jacket. Ownership of really good clothes has also been part of their education in the history of fashion. Hanging in a back office is a rack jam-packed with part of their huge hoard of vintage clothes. “I couldn’t believe what they did when I texted in a panic about having nothing to wear for my audition for Gatsby,” says actress Carey Mulligan (cast to play Daisy Buchanan for Baz Luhrmann), laughing. “I was hoping they’d send me some things from The Row, but then these huge boxes arrived—Ashley’s entire collection of thirties vintage dresses.” Apart from frequently wearing their own things (and lending them to friends), the girls study them for inspiration. The layered lace slipdresses and paillette-patched tunic dress they’ve designed for fall are the upshot of their forensic interest in traditional technique, and how to modernize it for today.

Of their formative influences, Mary-Kate goes off into vivid detail about watching how women around them dressed. “We had our observations about fashion changing, when it went from being so eighties to the slipdress and the dark lip. We’d see students coming back from college in grunge. And then Lori Loughlin [Full House] had all this great Donna Karan.” It was around the time of the Gaultier menswear pinstripes. Then it hits: Grunge-era dressing is still the basis of their look today—all that skill they have in layering dresses, sweaters, tailoring, the constant, free-form experimentation and the seeing of possibilities in repurposing, rescaling, and mismatching things. But Mary-Kate and Ashley Olsen were born in 1986, and Marc Jacobs’s grunge collection for Perry Ellis came out in 1992. So this was when they were six? They nod, expressionless.

You often get pulled up by that kind of shock around the Olsens, but that, really, is the least of how surprising they are as survivors of childhood fame who have extracted and reapplied the positives of their experience to invent themselves as highly effective adults. The critical-approval level The Row has reached this year is only, in their minds, the threshold of what they want to attain. Asked how they see their future, the answer is stunning. “I want to run a studio,” says Ashley thoughtfully. “I’d probably like to manage other people on their brands. It could be an artist. A young designer. It could be an existing brand.” Had that been spoken by any other person of 24, you’d put it down to sweet, juvenile dreaming. But from a pair with their kind of assets and business savvy? Ten years hence, it would not be surprising if the tiny Ashley and Mary-Kate Olsen turned out to be two of the largest players in mid-twenty-first-century American fashion. “The thing about us,” Mary-Kate says, “is we think big. Huge.” After all, in 2021, they’ll still be only 34.