Introduction Dressing is the fourth bodily function. After breathing, eating and sleeping -- and excluding a couple of delicious optional extras -- one of the fundamental pleasures of the human body is to clothe it. Which makes fashion -- it''s closest relation -- pretty important. The history of fashion touches everyone in its orbit. It runs far, far deeper than hemlines, silhouettes and colours. It is intrinsically caught up with social mores and mood changes in everything from food to mannerisms, music to sex. It lives and exists not only as one of the most ravishing and compelling of entertainments but as the surest indicator of time. Humour has always been part of its charm.

Throughout the twentieth century, Vogue has acted as a visual filter. Each season designers have thrown ideas into the air and Vogue has caught them and sprinkled them over its pages. It has always been down to the century''s social animals -- and significant figures -- whether designs transcended history or froze in suspended animation. Diana, Princess of Wales, had everything: genetic perfection, model dimensions, royal connections and the mystique of a silent-movie star. Add fashion, and the result was that she became the most photographed woman on the planet. In 1909 electricity was a new sensation, and it was shocking if a woman showed an ankle. By 1916, if she smoked in public, Vogue concluded, ''She must be an actress.'' If she wore red lipstick, she was the next best thing to a prostitute.

The wearing of a veil had orgasmic powers. Trousers were slammed as ''audacious''. If bumsters had been around, Alexander McQueen would have been locked up and labelled certifiable. Today, following the new millennium, no one bats an eyelid if dresses skim the nipples, navels are exposed and the bottom half of the buttocks are aired to ancient relatives. Nudity -- the natural conclusion -- will never be in fashion, not just because the weather wouldn''t allow it, but because it is the only style that would put the whole industry on social security. Ever since Eve wore a fig leaf, fashion has been associated with two things: defining sexuality and committing outrageous behaviour. Even fastenings aren''t immune. Consider the zip -- ''Zippergate'' -- a little metal fastening that almost brought down the president of America in 1998.

The biggest change has been in the status of the designer, who until the 1950s was considered a dictator, then a director and a suggester. Now he or she airs their opinions, controls huge empires and emblazons their name across every part of your anatomy. In turn, we want to see where they live, hear what they think, find out how they function. We sleep on their pillowcases, pull their curtains across our windows, spray ourselves with their scent: the most potent way to get style under the skin. The fly-past of designers'' behaviour throughout the last century is a seminal lesson to those who are thinking of taking up fashion design professionally. The most financially successful designers have brilliant business partners; the most creative have a single vision; the most famous are those who either have visionary tendencies or big mouths. Sometimes both. Then there are the handful of geniuses who put beauty and art before everything -- and inevitably ended up with nothing: the great Orientalist, Paul Poiret, once held the fashion world in the palm of his hand; the brilliant Ossie Clark, who could cut like a dream but couldn''t handle his own talent; Charles James, who was posthumously revered, but spent his declining years in New York''s seedy Chelsea Hotel with sketches, toiles and an Afro wig for company.

Passion and fashion -- unless there is a business brain in the frame -- just don''t mix. Age and body shape are part of the fashion template. In 1909 the face said 20, the waist said 15, the bosom 50. Flappers started smoking furiously in an attempt to echo the streamline shape of a greyhound. By 1960 there was the ludicrous situation where women of 40-plus were dressing like 10-year-olds. A hundred years from now, fashion historians flicking through this book, en route to a fortnight on the moon, may assume that millennium woman looked like Kate Moss. We don''t. Today, there is more choice than ever.

Status symbols on every seam. We are in a world of international fashion, but the elegance on the street has gone. The skill that required time, talent and a steady hand reached its peak of perfection in the 1950s and went rapidly downhill after the advent of television. Before 1960 women were fitted by their dressmakers. Now we make our own decisions on what size we are. Not wise. As Jean Muir once observed, ''People make pictures of themselves that other people have to look at.'' For fashion, read: prediction.

In the 1920s Cecil Beaton imagined that nuns would wear cubes on their heads and brides would wear bodysuits. In the 1960s Yves Saint Laurent said he would prefer taking a pill to actually eating a proper meal. He was not alone: in the mid-twentieth century almost everyone believed that by the year 2000 we would be wearing spacesuits to the office and would be coming home to have our dinner with a robot. What of the future? American minimalist Geoffrey Beene has been saying for years that ''the fundamental change will happen when the chemist meets the artist''. We already have temperature-sensitive and virtually indestructible fabrics. In the future, pundits predict clothes with in-built mobile phones; shops where we don''t rifle through rails but pick prototypes, and our measurements are drawn up on a computer. No doubt, one day, someone will invent a range of skirts that have meaningful conversations with washing machines. Designers are currently floating the idea of fashion shows on the internet.

But can fashion editors exist in a world devoid of gossip, seating arrangements and air kissing? Virtual reality in solitary confinement? Highly unlikely. For fashion is not -- and never has been -- about the clothes. It''s about people. Until genetic engineers decree otherwise. As long as the average human body is made up of four basic components -- one head, two arms, two legs and fleshy undulations in the middle -- fashion will continue to excite and delight within those strict, but endlessly fascinating, perimeters.