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On July 5, 1946, less than a week after the United States detonated an atomic bomb above tiny Bikini Atoll in the South Pacific, a Frenchman named Louis Réard — an automobile engineer moonlighting as a fashion designer — introduced to the sunbathing public what was billed as the world’s smallest swimsuit. Réard called his creation the bikini, a name inspired, he later said, by the sight of women rolling up their bathing suits in order to acquire a more complete tan.
Two-piece swimsuits had, of course, been around for a long, long time before Réard came along. Greek urns and mosaics created more than 3,000 years ago depict women athletes wearing two-piece outfits. But Réard’s genius was to devise a garment, out of as little fabric as possible, that one could still legally wear in public.
He marketed his new fashion brilliantly, as well — pronouncing, for example, that a bathing suit wasn’t a true bikini unless both pieces could be pulled through a wedding ring.
Here, LIFE.com offers a celebration of a bathing staple that, through the years, has enjoyed — and endured — a dizzying array of permutations while always remaining, unmistakably, itself.
Some of the early photos in this gallery depict two-piece bathing suits that might, at first glance, look like bona fide bikinis — but, in Réard’s eyes, would not fit the bill. After all, can be wearing a genuine bikini if, say, one’s bellybutton is covered by a swath of nylon, no matter how elegant or tasteful that swath might be.
Bikinis are not for everyone. There are, thankfully, as many styles of bathing suit as there are human body types and temperaments. That said, it remains incontestably true that few sights can evoke thoughts of summer’s delights with quite the same visceral punch as the unmistakable silhouette of Monsieur Réard’s ingeniously simple, timeless design.