Back when it referred to albums by bands that couldn't or wouldn't get a major label deal, indie music was easy to define. Today, hours could be spent debating its meaning. It may be an ethic, a genre, or a concept. Or maybe it's just a term of endearment arbitrarily applied to bands beloved for their unwillingness to conform.

Whatever exactly it is, Rilo Kiley is at the forefront of its movement into the mainstream.

The Los Angeles-based foursome, which bounces around from country-folk to pop-rock and is best known for Jenny Lewis's sweet vocals and deceptively dark lyrics, once earned most of its buzz on music blogs. By the end of 2004, its most recent album, More Adventurous, was finding its way onto best-of lists everywhere from Rolling Stone and Spin to Entertainment Weekly. Meanwhile, the band has managed the unthinkable - making the switch to a major label without losing hypersensitive indie fans.

"Initially, I was a little concerned because the independent community has really embraced us and we've grown up with it and I didn't want it to appear like we were jumping ship - which we weren't," Lewis says of signing with Warner, which allowed the band to set up its own label under its umbrella before recently re-releasing More Adventurous directly. "But this is an extension of one of our early dreams - creating our own label, finding distribution, so it doesn't feel entirely unnatural."

Suggesting that solo careers on smaller labels have allowed her, guitarist Blake Sennett and the other members to "maintain our independent roots," Lewis rejects the notion that Rilo Kiley is fundamentally changed by the Warner deal. "I think it matters less and less, she says. "And at a certain point you feel limited and you want to be able to reach more people. Blake and I have been writing together for nearly a decade, so it really has felt like a natural progression."

Certainly, the chemistry that fueled 2003's much-lauded The Execution of All Things doesn't appear to have been altered much in recording More Adventurous - and that includes the sometimes stormy relationships between members. "It's always difficult for us - this album was no different," Lewis says. "We're a very close-knit family, and we really love each other, but we also really hate each other sometimes. Every album has had its ups and downs."

However it came about, it's no surprise More Adventurous has appealed to indie diehards and mainstream audiences alike, with the band recently drawing raves playing to its biggest-ever audience at the Coachella Festival (an experience so "mind-boggling" the flame-haired frontwoman literally can't remember anything about it). Whether Lewis is leading the band through the romping, politically aware It's a Hit, or sounding like Patsy Cline on the countrified I Never, Rilo Kiley's eclectic sounds have something for everyone. And while the shift away from shared vocals has irritated some critics, it's given her poignant lyrics - which she calls her "personal obsession" - the centre stage they deserve.

Much more than the spoils of big-label success, the biggest threat to Rilo Kiley's future may be the divergent talents and interests of its members. Each seems to have an array of side-projects, and Lewis - who previously guested with The Postal Service - will soon branch out with a solo album.

But for now, the formula is working. "We need to maintain our autonomy and then we need to be able to come back to Rilo Kiley to collaborate," Lewis says. "Sometimes it can be rocky - you know, 'Does she like that band better than this band?' But I think in the end we all know that this is what we're doing right now, and we look forward to coming back and working together."