Fashion moves fast, and retailers react by moving even faster: Already, fall clothes are on the racks and in windows – while we’re still sweltering outside. But things are different at Foley + Corinna, the ultra-hip boutique on the Lower East Side.

The shop, visited by the likes of Liv Tyler, Jessica Simpson, and Stella Mc-Cartney, is a joint effort by two friends with two different approaches to fashion. Dayna Foley designs and creates clothes under the label “Foley.” Anna Corinna buys vintage clothes – from Victoriana to ’80s flash – that are meant to be worn today, not preserved and collected. Right now, they’re mixing and matching for hot summer days. And they’re only just starting to think in earnest about fall.

“Everybody’s putting their summer stuff on sale,” said Ms. Foley, who’s just beginning to acknowledge the changing of the seasons.

That Foley + Corinna works independently of the fashion industry’s timetable is just one way in which this boutique keeps ahead of the trends. Together, the stylish team watches very closely what their customers are seeking out.

“It’s about paying attention to what the girls who come in are wearing, talking about, or picking up,” said Ms. Corinna. “The girls who shop here are all so beautiful and ahead of it. I give them a lot of credit.”

With the information they glean, they’re able to tailor the merchandise accordingly. Ms. Corinna will put out vintage clothes that fit a given aesthetic – be it “cowboy courtesan” or whatever new look is emerging this week. “I’m an eclectic buyer. We try to put out new stuff every week or so. There is always new stuff here,” she said.

Likewise, Ms. Foley keeps her production cycle small and responsive. “We’re not going to make 1,000 of something. We’ll make 10, and if people like them, we’ll make more,” the designer said.

And because of the small scale of the projects, ditching a batch of something isn’t a major loss. “If she doesn’t like the way something is turning out, she can pull it off the machine,” said Ms. Corinna.

When starting out to design her pieces, Ms. Foley takes into consideration the talk of certain trends, but she treats them with caution. Trends, after all, are fickle things. And they can get played out before they even begin. “As soon as it comes, then no one actually wants to wear it,” she said. “At one point, people were saying ‘Prints, prints, prints.’ Immediately, I said to myself, ‘Do not go into that.'”

Ms. Foley and Ms. Corinna met in the early 1990s when both were selling merchandise at flea markets. They realized that they had a similar aesthetic and decided to work together. Ms. Corinna, who grew up in upstate New York with parents in the antiques business, now lives in Williamsburg, Brooklyn. Ms. Foley, who grew up in Brooklyn Heights, lives just three blocks away from the store.

The close proximity to their store – and their clients – allows them to constantly keep tabs on what the trendsetters are wearing. “We’re in New York City, on the Lower East Side,” said Ms. Foley. “I used to never go above 14th Street. Now I never go above Houston.”

But very often their clothes do. While the shop functions as their headquarters, Ms. Foley and Ms. Corinna also run a wholesale business that sends the Foley line as far uptown as Barneys and as far out of town as Nordstrom.

The fun of going to the shop, however, is the ability to put together new and old clothes in a way that expresses your own style. The clothes in the shop are grouped according to color, and while it’s fun to browse through, this is a shop where it pays to rely on the shop girls. “You really can’t see all of it. The sales girls have to have a good knowledge of what’s on the racks,” Ms. Foley said.

Because the merchandise changes so much, pieces come and go. But on a recent afternoon, Ms. Corinna suggested pairing a white tank top with wide straps and a flowing waist ($120), made by Foley, and a sheer vintage capelet ($75). For the bottoms, there are jeans by Martin and Notify or wide-leg linen pants by Foley ($250). The shop includes an array of jewelry ($35 to $95), vintage shoes ($75 to $125), and handbags designed by Ms. Corinna ($55 to $125).

The shop is decorated to look like a glamorous, yet inviting, boudoir, with hand-painted pictures of birds, butterflies, and flowers all over the walls. The space, at 114 Stanton St., was a new development this summer: The girls grew out of their former digs down the street at 108 Stanton. Also nearby is Foley + Corinna’s men’s shop (148 Ludlow St.), which carries vintage clothing and accessories, plus brands including Steven Alan, Rafe, and Wrangler.

For fall, Ms. Corinna is thinking along the lines of flowing styles with less embellishment and a Victorian edge. But that’s really just the beginning.

Foley + Corinna (114 Stanton St., 212-529-2338).