WIMBLEDON, England — Who says the oldest and most tradition-laden of tennis' major championships doesn't change with the times?

There is, at long last, a retractable roof atop Centre Court at Wimbledon this year. Video review of line calls and equal prize money for men and women came along ages ago (well, OK, in 2007).

Rest assured: They still use grass courts, they still make the players wear white, and they still schedule a day off on the middle Sunday of a tournament first held in 1877. Here's something else that stays the same at the All England Lawn Tennis and Croquet Club: Venus Williams and Serena Williams are the women to beat.

Venus, in particular. She's won five titles, including the last two, at Wimbledon, which begins Monday. Serena has won this Grand Slam tournament twice, beating Venus in the 2002-03 finals and losing to her in last year's championship match.

The names and faces at the top of women's tennis keep switching, as players emerge, then recede or retire — Martina Hingis, Justine Henin, Jennifer Capriati, Lindsay Davenport, Amelie Mauresmo. The Williams sisters? One or the other — or both — participated in eight of the past nine Wimbledon finals, and they're the top picks of British oddsmakers this time.

"Serena and I, we often talk about that: 'Wonder what happened to them?' We're still here — and we're not leaving," Venus said Sunday, two days before she'll open her attempt to become the first woman since Steffi Graf in 1991-93 to win three consecutive Wimbledon championships.

"It's been a real blessing to have the success that we've had and to be able to be still playing great tennis at this point, obviously with the outlook of still playing great tennis for years to come," she continued, noting she wants to enter the 2012 London Olympics. "I don't see anything changing for a while."

As the defending women's champion, No. 3-seeded Venus is slated to play her first match Tuesday on Centre Court, against Stefanie Voegele of Switzerland. A statistic for Voegele to ponder: Her career Grand Slam record is 0-1, and Venus' is 180-38.

Second-seeded Serena starts on Day 1. She faces 154th-ranked Neuza Silva of Portugal on Centre Court after Roger Federer meets Yen-hsun Lee of Taiwan in what, in theory, could be the first match in the 132-year history of Wimbledon to be played indoors. There is a 20 percent chance of rain Monday.

The new translucent roof on Centre Court, an arena that dates to 1922, takes about 10 minutes to close and should forever eliminate those dreary days when zero tennis is played because of rain.

"'Update. Don't be late.' That's my motto," Venus said. "So I think the roof is good."

Some players question whether it's fair that only matches on the main court can be carried out when Mother Nature messes with the tournament, but count Federer among those in favor of the roof.

"Might be more intimate," said Federer, who lost a five-set thriller of a final last year to Rafael Nadal, a no-show in 2009 because of bad knees. "You're not looking for rain, (but) looking forward to experience it."

Federer begins his bid for a sixth Wimbledon championship, and a record-breaking 15th major title, a couple of weeks after completing a career Grand Slam by winning the French Open.

Neither Williams fared that well in Paris, with Venus losing in the third round and Serena in the quarterfinals. Venus also was upset in the second round at the Australian Open in January, and she's won only five of her past nine matches.

But form never seems to matter for the sisters when the season shifts from clay to grass, even if they opt to skip tuneup tournaments between the French Open and Wimbledon. In 2008, for example, both lost in the third round at Roland Garros, then forged an all-in-the-family final at the All England Club.

Several years ago, Serena did intend to try a more traditional preparation.

"I didn't play. It rained, like, 12 out of the five days I was there," she recalled with a laugh.

So instead, she and her sister — Venus turned 29 Wednesday; Serena is 27 — fly home to the United States and work on hard courts, then get used to the grass with joint practice sessions at Wimbledon, something they did Sunday morning.

Venus' Grand Slam trophy collection was amassed mainly at Wimbledon; she won the U.S. Open in 2000-01. Serena, meanwhile, has at least one title from each of the other three majors, for a total of 10. Venus was asked Sunday why Wimbledon is by far her best Grand Slam tournament.

"Everyone asks that. My answer is: why not?" Venus said. "Everybody wants to know the secret. There is no secret."

A few moments later, she was slightly more forthcoming, saying: "You're rewarded for playing aggressively, and that's definitely how I play: aggressively. I have lots of rewards."

Yes, she does, and while it might not be surprising that Serena would say her sister "has proven herself to be the best grass-court player in our generation," praise for Venus comes from all corners, including 2004 Wimbledon champion Maria Sharapova.

"She has a very big game, a very powerful and steady game. You know, her serve is a big weapon. She uses a lot of her strengths on this surface really well. And she's just able to do it year after year after year," Sharapova said. "Certainly with her past results, I definitely think she's the favorite."

Some wonder whether Venus should be seeded No. 1, instead of top-ranked Dinara Safina, who is 0-3 in major finals.

"I'm not sure it's right at all that Dinara Safina is the top seed at Wimbledon. Venus has won it five times," said Mary Carillo, a former player working on ESPN2's telecasts. "Especially on grass, which is the surface where most people think the seeding committee can tweak and make changes, I truly believe that Venus deserves to be seeded 1."