Agnes b. is probably France's best-known designer of chic, no nonsense, ready-to-wear clothing, but she has never once advertised, doesn't take part in catwalk shows, doesn't hang out with the fashion pack and doesn't even seem that passionate about clothes. Her business, which has made her one of France's wealthiest women, has an annual turnover of around Ffr1 billion. Agnes b. describes herself as having had a classic French upbringing, with lots of cultural exposure from an early age. Wishing to be an art curator when she grew up, by a series of coincidences she instead became a fashion editor at Elle magazine. "I didn't like the fashion at the time," she says simply, "so I started making my own clothes." As the business - run from her flat - took off, she hijacked the B from Bourgeois, her first husband's surname, made it lower case and by 1975 had opened her first shop in Paris.

She now has 110 boutiques worldwide (50 of them in Japan) stocking clothes for women, men and children together with the Lolita teenage range, as well as a coffee shop, an interiors outlet, an art gallery and a film production company. "I don't think clothes are that important anyway," she says. "They should be practical and comfortable; you shouldn't have to think too much about them. They should fit in with the wearer as opposed to overwhelming him - that's why I design simple clothes, so that they don't stand out, but rather that the individual's own personality overrides whatever he's got on."

Dressed in a loose-fitting black trouser suit with a pristine white shirt, Agnes b. is an advertisement for what she does, not only because she looks both hip and classy (as well as the clothes being very well-cut and made) but also because what this 57-year-old grandmother is wearing so stylishly gives no indication of her age; these pieces would look equally well on a woman of 30 or even 20. "When I hear women say, `I'm too old to wear that,' it makes me really sad," she remarks. "That's why I try to make clothes for everyone." The Lolita line, for example, carries many items which are repeated in the womenswear range. Agnes b. designs with friends, children and those around her in mind, basing her ideas on what she sees rather than what she imagines. She has no feminine ideal or muse, other than her own grandmother. Nor does she have any interest in fashion's seasonal merry-go-round; she eschews the Paris catwalk and has no clue what other designers are showing. "I don't believe in new outfits every season," she explains. "I have no inclination for the ephemeral. I like to invest my time in things that last, that are nice to keep so that you buy one thing and add it to what you already possess." This philosophy has served her well; customers still request the T-shirt that she has been selling for 12 years and the snap-closing cardigan which has been on her shop shelves for nine.

AGNES b. describes her work as intuitive rather than inspired by direct reference. For winter 1999, for example, she had a yen for red and grey in solid blocks with lots of square and rectangular silhouettes. She then realised that these looked like paintings by the Russian Suprematist artist Kazimir Malevich, whose work she greatly admires. However, she was also vaguely aware of Chanel's style, not so much in terms of the latter's own designs but rather the way she had dressed herself as a young woman, putting unusual clothes combinations together in a very modern way. For the present season, there is a touch of 1950s nostalgia about Agnes b.'s designs with off-the-shoulder knits in red and pink combinations, classic pedal-pushers, wide-legged sailor's pants in navy and starchy white, filmstar raincoats in modern fabrics and sweet sleeveless round-necked shirts in pale pink and lilac, which look terrific teamed with one of the umpteen choices of black trousers. In addition, there are boxy red dresses and below-the-knee jersey/silk skirts which are actually flattering (instead of just clingy), all alongside the usual array of T-shirts, cardigans and vest tops.

What stands out in this, and every, collection is the quality of fabrics - mostly natural - and of manufacture. Agnes b. insists all her products are French-made, in spite of the country's high labour costs. Wanting to support domestic workers (she makes a point of getting to know all her factory staff personally), as well as doing her bit for the local economy, she is also insistent on certain levels of quality which are not as easily fulfilled in Asia. "Doing her bit," is a repetitive theme for Agnes b. In order to pursue her own artistic interests as well as to help artists find their feet, she set up her own gallery in 1984; here she represents Irish artist Paul Seawright alongside Martin Parr, Cathy de Monchaux and Kenneth Anger. She was invited to present last year's Turner art prize in London. She has also set up a film production company called Love Streams to assist struggling young film-makers. One of the results of this, the controversial Seul Contre Tous, had a run in Dublin last month, and her latest cinematic offering Peau Neuve has just won the International Critics Award at the Cannes Film Festival. Do all these extra-curricular activities point to a waning interest in clothes design? Agnes b. shrugs her shoulders and says, "I only started doing clothes while I was waiting to do something else." She pauses and then adds with a giggle: "I'm still waiting to do something else."