The old query "Tennis anyone?" may now be replaced with "Tennis everyone!"

Tennis reached its peak in popularity during the 1970s, when more than 30 million people played. Participation declined in the '80s and '90s even as the professional circuit blossomed.

But the game has been on the upswing in the 21st century, with participation growing by 43 percent since 2000, according to a study conducted by the Sporting Goods Manufacturer Association and Physical Activity Council.

Part of this growth is due to promotional efforts by the U.S. Tennis Association, which has kept the sport strong despite the struggling economy. The game has come a long way from Henry VIII's Tudor-era Hampton Court Palace, where it was played only by the aristocracy on the Royal Tennis Court. On Monday, talent from all over the world will descend on the Tennis Center in Flushing Meadows, Queens, N.Y., for the U.S. Open Tennis Championships, which continues through Sept. 12.

What has grown along with the fan base is an interest in the on-court ensembles and gear, ranging from tennis superstar Venus Williams' designs to Burnout T-shirts and Henry Brown bags.

"In women's tennis apparel, fit has become as important as design," said Paul White, head of merchandise at the USTA.

A streamlined fit to show off those lean and buff bodies is what it's all about. "Clean designs that are sized properly have stood tall in 2010," he said.

The quarter-pleat skort for women and reversible shorts for men are very popular among the tennis-playing public, Mr. White added.

"From a lifestyle perspective, the Burnout T[-shirt] continues to trend well and we've added our own evolution with [images of] flaming ball burnouts all over the garment," he said.

Traditionalists will be happy to see Lacoste polo shirts with that famous alligator (it's really a crocodile) emblem is still at the top of its game, as is the other iconic emblem of country club classics, Ralph Lauren's polo player. Polo Ralph Lauren is in its sixth year as official sponsor of U.S. Open apparel.

The 130-year-old French company Babolat has found a big following for its tennis rackets and shoes. Mr. White says Wilson also has gained attention with its BLX racket.

"An ad campaign for the BLX featuring Roger Federer serving as a 'tennis shrink' has gotten a lot of laughs," he said.

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