The Indigo Girls began singing together during college with no aspirations other than having fun. Three decades later, Emily Saliers and Amy Ray are going strong as one of the most recognizable folk-rock duos around. This week, they share the Wolf Trap stage with Joan Baez.

"We toured with Joan about 10 years ago and have known each so long that we've become good friends," Saliers said. "When the idea of this tour came up, we jumped at the opportunity because we love her as a person. She has such energy and spirit that when we toured with her at colleges, some of the kids didn't realize how powerful she was until she began to sing. They fell for her immediately.

"Amy and I will open the show with favorites from our discography, some old, some new, then Joan will join us. We're excited about our band, the Shadowboxers, a group of young guys who went to college at Emory University. We love the fact that in this show we're stretching the generations."

Both Saliers and Ray grew up in musical families and sang in church choirs. Although neither had formal training other than a few composition courses, they began singing professionally while in high school. After taking a year off to attend college out of town, they returned home to Atlanta. By the time they left Emory, their success singing locally convinced them they could make a go of the duo. Fourteen studio albums and four live album later, they are happy about launching their own recording company several years ago.

The Indigo Girls and Joan Baez
» Where: Wolf Trap's Filene Center, 1551 Trap Road, Vienna
» When: 8 p.m. Wednesday
» Info: $42 in-house, $28 lawn; 877- WOLFTRAP;

"The advantages are that we don't have to ask permission and we don't waste any money," Saliers said. "We have a great distributor in Vanguard Records, so we aren't part of the big distribution machinery that can hold you back."

In addition to performing together, both have sidelines. Ray has released several solo albums and founded a nonprofit organization to help independent musicians. Saliers, a professional author and sometime collaborator with her father, a theology professor at Emory, satisfies her foodie whims by investing in restaurants.

"My first investment was in the Flying Biscuit Cafe so people who slept late could have breakfast all day," she said. "Currently, I own Watershed restaurant in Atlanta which just opened in a new location. I love the way Southern food brings people together."

High on their list of projects are causes to aid the environment, gay rights, the indigenous community of Native Americans and the National Coalition to Abolish the Death Penalty. To support the causes they cherish, they aim their T-shirt campaign at immigration and anti-death legislation.

"We love singing together for our fans so much that we let them tape our shows, so long as they only share them with friends for fun," Saliers said. "This sets the tone. We grew up sharing tapes, and we know how much fans love to do this. Amy and I are inspired to sing together because we're old friends. I love her voice and the powerful way we're in synch about everything. This tour is very special because we both love and admire Joan."