WIMBLEDON, England - Two simple words at the end of a June 7 tweet said it all: "Serena's back!"

And Venus is, too.

Yes, as Serena Williams announced to the world less than two weeks ago, the most successful tennis-playing siblings in history are returning from lengthy layoffs right on time for Wimbledon, where they just so happen to have won nine of the past 11 singles championships.

For Serena, it will be her first Grand Slam tournament - and only second event - since she took home a second consecutive title from the All England Club in July 2010. Her nearly yearlong absence resulted from a series of health issues, including two foot operations and blood clots in her lungs, that she said left her depressed and "on my deathbed." Venus, meanwhile, was sidelined by a hip injury from January until June.

All eyes will be on them when the grass-court Grand Slam tournament begins Monday.

"I feel like we've been on a similar road together. Her road hasn't been as arduous or as long as mine, but I know what she's been through coming back," Serena said when she made her 2011 debut at a tuneup tournament this week in Eastbourne, England. "We've been really enjoying our time just getting back together and practicing next to her and looking over and seeing her play so well. I'm like, 'OK, I've got to do better.'"

There are, to be sure, other plot lines worth tracking during the fortnight.

Among them: Can Roger Federer make a real run at a seventh Wimbledon title? Can Rafael Nadal extend his recent excellence to five titles in a span of six Grand Slam tournaments? Can Novak Djokovic recover from the end of his 43-match winning streak to win a major title other than the Australian Open? Can Andy Murray finally - and mercifully - put an end to the locals' 75-year wait for a British male champion at the All England Club? Might No. 1-ranked Caroline Wozniacki win her first Grand Slam title? Could China's Li Na win her second in a row? Will Maria Sharapova end her 3?-year major drought?

But the biggest curiosity, at least at the outset, is: How will the Williams sisters do?

"It will be interesting to see how they come back. I think it's interesting for the tour. It's a good story," Federer said Saturday. "It's been an up-and-down, bumpy road for the women's tour as of late. But we'll see now how it goes here with the sisters back in the game."

Part of the interest stems from wondering how much longer they'll be around. Venus turned 31 on Friday; Serena will be 30 in September.

"Whenever they enter a Grand Slam tournament, it's double the excitement and double the intrigue, I think, that they bring to the sport. They just bring a different level of tennis also, as far as the power and the emotional content," said ESPN2 analyst Chris Evert, who won 18 Grand Slam titles.

"It would be monumental in my mind if Serena pulled off a win," Evert added. "I personally don't know how it's humanly possible for someone to take a year off like that and have gone through what she's been through physically with her ailments and ... it would almost shock me if she did. But knowing Serena and the way she's come back before, you can never count her out."

Evert - who said she never was away from the tour longer than four months - is one of only five women in tennis history who have won more major championships than Serena's 13. The others are Margaret Court (24), Steffi Graf (22), Helen Wills Moody (19) and Martina Navratilova (18). Among active players, of course, Serena ranks No. 1, followed by Venus with seven.

No one else in this year's Wimbledon women's field has more than three Grand Slam titles (Kim Clijsters has four, but she pulled out with a foot injury).

Indeed, it's remarkable to examine the measurable ways in which Serena and Venus have dominated women's tennis, in general - and the All England Club, in particular - across the years. That's why Serena is seeded No. 7 at Wimbledon, despite being ranked 26th; Venus is seeded 23rd, despite being ranked 33rd.

"You know," Sharapova said, "they're obviously the ones to beat on grass."

Not only has Venus won five titles at Wimbledon, and Serena four, since 2000, but they've also produced four all-in-the-family finals there in that span. They've played in a total of eight all-Williams Grand Slam championship matches, with Serena holding a 6-2 edge.

At Wimbledon, Venus is 68-9, Serena 57-7. No one else in the 2011 draw has more than 27 match wins there.

"Obviously," Wozniacki said, "no one wants to play them."

Overall, Serena has been to 16 major finals, Venus 14. No one else in the draw has reached more than four.

As seven-time major champion John McEnroe put it: "I wouldn't minimize their chances."

Hey, at least one British bookmaker installed Serena as a 3-1 favorite to win Wimbledon.

The interest generated by the sisters' rise to the top of their sport is widely pointed to as the reason for the U.S. Open's decision to move its women's final to prime time in 2001. Venus beat Serena that year for the title, and nearly 23 million viewers tuned in to the CBS broadcast, giving their match the largest TV audience of any program that night, including a game between traditional college football powers Notre Dame and Nebraska.

The last major tournament, the French Open, was the first Grand Slam since 2003 without Serena or Venus - and chaos reigned. It's the only French Open in history where none of the top three seeded women reached the quarterfinals, and it left some looking forward to when the sisters would pick up their rackets again.

"I'm sure when they come back, they'll come back ready. That's how they do it. Tennis has been pretty spoiled by their success and they're pretty special, two special sisters," top-10 U.S. man Mardy Fish said in Paris. "And when they're not around, you can feel it. You can feel at a Grand Slam when they're not here, and so I think everyone's hoping that they'll be back, better than ever, soon."

Serena lost in the second round at Eastbourne, a three-set struggle against the woman she beat in last year's Wimbledon final, Vera Zvonareva. Venus lasted one round longer.

They're not merely happy to be back, though.

They want to contend for more titles.

"I always believe in myself when I go on the court," Venus said. "And I'm not just here to look good on the court; I'm here to win every match I'm in."