There are many storylines to watch for entering the 2015 U.S. Open, but none come close to the achievements that stand before Serena Williams. Having already won the Australian Open, French Open and Wimbledon this year, the American enters Flushing Meadows with a chance to become just the fourth woman in history, and first since Steffi Graf 27 years ago, to win all four Grand Slams in a single year.

But as if that weren’t enough, victory for Williams will also put her level with Graf for the most Grand Slams in the Open era (started in 1968), with 22. Whether she completes the feat or not, discussion will be sparked about where Williams stands among the greatest female tennis players of all time. Here’s our personal top 10

Serena Williams

A the age of 33, Serena shows no signs of slowing down and, indeed, is on the verge of her greatest achievement yet.

Steffi Graf

It is no slight on Graf to no longer consider her the greatest of all time. The German dominated women’s tennis between 1988 and 1996, holding the No. 1 ranking for an extraordinary 377 weeks

Martina Navratilova

Few female athletes can match the enduring legacy of the women who left Czechoslovakia to become an American citizen and go on to claim a still-record 167 titles on the WTA Tour.

Chris Evert

Although Serena may change that in a couple of weeks, as things stand no female player has won more U.S. Opens than Evert’s six

Margaret Court

Serena still has some way to go before matching Court’s record of 24 Grand Slam titles, 11 of which were in the Open era

There are many storylines to watch for entering the 2015 U.S. Open, but none come close to the achievements that stand before Serena Williams.

Billie Jean King

The California-native’s impact on women’s tennis far exceeded her achievements on the court, having been the founder of the Women’s Tennis Association and a fervent campaigner for gender equality in the sport and beyond.

Monica Seles

Seles became the youngest-ever French Open champion in 1990 at the age of 16 and over the next two-and-a-half years incredibly added another seven Grand Slam titles.

Venus Williams

While she may not be able to match her sister’s achievements, Venus has had a superb career in her own right and it was her breakthrough on the tour at the turn of the century that truly ushered in a new era of power in women’s tennis.