The words "country" and "crossover" have gone hand in hand ever since Olivia Newton-John donned denim and sang "Let Me Be There," and probably before that.

In the current market, Taylor Swift is just a few fiddle strokes away from being Miley Cyrus, and Keith Urban could very well have been the next Bon Jovi.

But the new superstar duo of Jennifer Nettles and Kristian Bush, better known as Sugarland, take it to a different level by dipping into the indie-rock and dance-pop scenes. Sugarland covered R.E.M. and Pearl Jam on its album, jammed with Beyonce and even brought the B-52's to the CMT Awards.

"On my iPod I have everything from Johnny Cash to Beyonce to Eminem to Phoenix," says Ms. Nettles, surprising us with that last reference. "I have really diverse tastes in music. I think a lot of people do. I don't think music is as much about a lifestyle anymore as it used to be. You don't have to wear a certain kind of clothing to listen to country music. You don't have to look a certain way to listen to country or listen to rap. You can like it all."

Sugarland's success has clearly been in the country arena. It charts country, has toured with Kenny Chesney and Brad Paisley, and is part of the country megaticket package at the First Niagara Pavilion. But this duo, rooted in the Atlanta folk-rock scene, could have taken any number of turns along the musical path.

Sugarland was formed in 2003 by Mr. Bush (formerly of Billy Pilgrim) and Kristen Hall, and later added the namesake of the Jennifer Nettles Band, who bears a striking resemblance to Cameron Diaz, as its lead singer. Prior to that, going back to 1996, she was a member of Soul Miner's Daughter, another band that showed off her stunning bluesy pipes.

"When I first started out I did not see myself going that way," she says of country, "though I grew up around country, in country and was pretty much steeped in it being from south Georgia. However, I came to country first as a writer. I had been doing the singer-songwriter thing for a good 10 years before we started this project. At the time, I don't think radio was very healthy overall for the singer-songwriter. Pop music was very bubblegum, dance-driven and that's definitely not me. So I wanted to really focus on a place where I could really grow and develop my craft. That was, and I think still is, country music. Country music has always been about the songs."

Once in Sugarland, the climb to success was rapid. The trio's first single, "Baby Girl," hit No. 2 on the country charts and stuck around for 46 weeks. The second album, "Enjoy the Ride," which saw the departure of Ms. Hall, produced two No. 1 singles, "Settlin' " and the Grammy-winning "Stay," which was accompanied by a video that rivaled or even surpassed Sinead O'Connor's "Nothing Compares 2 U" in its emotional force.

"That was the raw, sort of sparse, exposed emotion that we were going for and we used that [video] as a reference -- very simple and very effective. At the time I was going through a big personal transition so I was really raw emotionally in general. So to sing a song like that, it wasn't very hard for me to access a place of that kind of vulnerability."

Sugarland's third album, 2008's "Love on the Inside," produced three more No. 1 country singles, including the playful "All I Want to Do," accompanied by Ms. Nettles' surf video, the country power ballad "Already Gone" and "It Happens," a sort-of upbeat ode to oops. The group grabbed Grammys for Best Country Song and Best Country Performance by a Duo or Group and even ended Brooks & Dunn's nine-year streak at the ACM's by winning Vocal Duo of the Year.

Along the way, Sugarland learned the ropes playing to the Chesney/Paisley crowds in huge venues.

"I've always enjoyed as we've been out with people, watching, learning, seeing how they handle their situations and how they work their crowds," she says. "Everyone has a different take on it, and in country music there's a bit of a system of mentoring that happens -- where people are welcoming and say, 'Come in, see how we do this and take what you like and develop your own around it.' So I'm so appreciative for all those opportunities.

"Where Kenny is concerned, it gave us a chance to go out and be in front of a sta-di-um. Hel-lo ... Can I just point out that there are probably a handful of acts that have been able to perform in a stadium in the past four years. Let's think about the headliners: I know the Stones have done stadiums, U2, Kenny, maybe Springsteen. It's a small list, so to get the chance to open up, that kind of stuff is invaluable experience as an artist."

Sugarland's maiden run as an amphitheater headliner comes in advance of its fourth album, "The Incredible Machine," which won't be ready until October. The singer describes it as up-tempo and a step forward for the duo.

"We're lucky in that our fans have come to not only expect, but anticipate and even demand, our growth as writers and artists -- our evolution. I think there are some artists in every genre whose role it is to hold the line and sound just like they sounded from the first day that they come out -- and many of them don't write their own songs, so they stick to a certain kind of sound for themselves. And we need those. We need all of these in this big family. There are other artists whose job it is to push and evolve the genre and that I think is where we come in. We have people who come up to us all the time and say, 'We don't like country music but we love what you do.' I say, 'You are who we write records for, my friend. Come on in, the water's fine.' Kristian and I have lots of different influences and it's fun for us from a diversity level to draw on those, still staying who we are because obviously it's our writing, it's my voice, it's not a departure, but we like to have growth with each record. I hope that the fans listen to this record and consequently say, 'It's not what I expected -- it was better.' "

Just as important to Ms. Nettles as hit singles and awards is knowing that the songs are making a personal connection with people.

" 'Stay' is one that always resonates and that people connected with so deeply. We've had people come with 'Settlin' and say, 'This helped me through my relationship or my divorce,' or we've had people come up for 'Something More' and say, 'This helped me quit my job. I was tired of doing it and now I'm doing this and I love it.' That is why I think music is powerful. That's why I write and perform is to connect with another human being, and either through listening to the CD or in the moment in the show have that person feel like that they are understood and hopefully feel not so alone, because it can be an isolating world out there. To connect with people and have them feel not so isolated, that's why you do it."

Critics Andrew Druckenbrod and Scott Mervis talk about music on "The Beat," available exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.