The biggest WTA-only tournament of the season kicks off with main-draw action on Monday in Charleston.

The Volvo Open, played on green clay, is celebrating it's 45th anniversary.

"If you look at the history of the tour, the tour goes back 45 years as well. So it runs hand in hand with the growth of the tour," tournament director Bob Moran said about his event. "We were one of the first events to be nationally televised and to offer $1 million in prize money."

The field this year features Madison Keys, Venus Williams, Johanna Konta, Elena Vesnina, Caroline Wozniacki and many more.

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Sloane Stephens won the title in Charleston last year, and though she's still injured, she'll return this week—on the sidelines for Tennis Channel.