"It was a time of creation and a really fun time in music," Stefani says of her debut album. "I'm really lucky that I got to live through that period.”

Gwen Stefani never planned on being a solo pop star, but in the early 2000s, her musical journey took an unexpected, fruitful turn.

After enjoying nearly a decade of stardom in No Doubt, Stefani and the rest of the band members decided they needed a break. The alt-rock group officially announced its hiatus in 2003; at that point, Stefani had already flirted with a solo career on a pair of collaborations, Moby’s “Southside” and the Grammy-winning “Let Me Blow Ya Mind” single with Eve. The latter effectively began her transformation from the darling of the ska-punk set to an urban pop princess.

“[Pop music] was cheesy to us," Stefani tells Billboard. "You know when you're a teenager and you have these rules you put on yourself? We were all about being in a band. But I started realizing how good some of that pop and dance music was. The music from high school became nostalgic -- it was the backdrop of my life.”

During No Doubt’s hiatus, that pop crown became securely positioned atop Stefani's blonde locks, once she threw herself into the world of ‘80s dance, new wave and freestyle that eventually became her first solo album, 2004's Love. Angel. Music. Baby. “When I went in to start working [on the record], I'd never written with anyone else outside of the band,” she says. “I didn't even know there were these writing circuits you could go on to work with the popular songwriters of the moment. Everything was new, and I felt really rebellious and outrageous to be doing it.”

The album finds Stefani confronting her insecurities of going solo (“What You Waiting For?”), closing past relationships while entering a new one (“Cool” and “The Real Thing”), and exploring her newfound admiration for Japanese culture (“Harajuku Girls”). Along with having No Doubt band mate (and ex-boyfriend) Tony Kanal by her side, the singer was also buoyed by an impressive list of collaborators who polished the record’s sound: Linda Perry, Dallas Austin, Andre 3000, Dr. Dre.

Along with proving that Stefani could tackle dance-pop just as effortlessly as alt-rock, Love. Angel. Music. Baby also helped lay the foundation for millennial pop girls to confidently dive into hip-hop and R&B. Fergie and Nelly Furtado followed suit two years later with eclectic, rap-leaning The Dutchess and the Timbaland-assisted Loose, respectively. Toward the start of the 2010s, artists like Kesha and Katy Perry channeled Stefani's pop kookiness through their vibrant outfits and sing-rap lyrics.

Despite her initial hesitation to go solo, Stefani's Love. Angel. Music. Baby was a huge success: the album debuted at No. 7 on the Billboard 200 chart, has sold 4 million U.S. copies to date according to Nielsen Music and earned six Grammy nominations, including one for album of the year. It also spawned a pair of top 10 singles: “Rich Girl,” another team-up with Eve which peaked at No. 7 on the Hot 100, and, more memorably, “Hollaback Girl," which topped the chart for four weeks.

Stefani says she was never expecting the album to skyrocket; today, she likens its success to an inexplicable yet overwhelming fashion trend, like Crocs. “I didn't know it was gonna be embraced the way it was,” she explains. “Plus, so many other things were happening in my life: I just got married [to Gavin Rossdale in 2002], went on my first solo tour where I actually had costume changes, got pregnant with my first baby, started [the clothing lines] L.A.M.B. and Harajuku Lovers. It was a time of creation and a really fun time in music. I'm really lucky that I got to live through that period.”

In a conversation with Billboard ahead of the album's 15th anniversary on Nov. 23, Gwen Stefani revealed the stories behind every track of Love. Angel. Music. Baby. -- from how she escaped her comfort zone to her love for bringing cultures together. (Note: the conversation has been condensed and edited for clarity.)

1. What You Waiting For?

StefanI: Linda [Perry] was the first person I went in the studio with. 4 Non Blondes was one of the first acts signed to Interscope, just like No Doubt. It was such a weird thing going in with a girl -- I never hung out with girls before, because I was always with guys. Linda could literally play every single instrument, sing, make tracks. I never did that before, I always worked to a guitar or piano. It was all new, and super intimidating. Linda wasn't, but I made her that way because I was so timid.

So we just sat there and I remember her seeing me from her perspective. She said to me, "What are you waiting for? Stop it!" I had gone home from the first session, came back the next morning and she had the track. We went into the booth and would trade off ad-libbing. It was a normal thing to do, but also super scary to have to channel melodies and sing in front of her. It was really fun because we came up with this crazy melody that was all over the place.

I look at a lot of these lyrics like they're God's work. They just came to my head. That song is quite masterful. It's such a weird blend of styles. It talks about being scared -- it was just so true to where I was at in that moment. When we were trying to pick the first single, the record company didn't want that song because it wasn't really for radio. It's very kooky and weird and punk. I didn't care. I didn't go into this record wanting it to be a hit. I was in a very artistic place where I was just like, "I have to do this. It has to be this song first, because it lays out the whole story." The record was a statement: the visuals, the Harajuku Girls. I had traveled the world, you know?

2. Rich Girl feat. Eve

Working with Eve [on 2001’s “Let Me Blow Ya Mind”] was one of the greatest things that ever happened to me. It opened me up to a whole different group of human beings. I was on the BET Awards, that was so cool! With No Doubt, we listened to reggae and ska -- it was in our DNA. But to be able to cross over to do hip-hop was another level. We watched it be born, so to work with Dr. Dre [who produced the song] was crazy! [Interscope Records co-founder] Jimmy Iovine was the one who made that happened. He always tried to cross-pollinate everybody. I think it was all these negotiations to try to force people to work together. It wasn't like Dre said, "Oh cool, let me work with Gwen!" But Eve told me that she really wanted me on a track.

“Let Me Blow Ya Mind” was so awesome, and we wanted to do another track together. Dre's the one who came to me with "Rich Girl.” I thought it was the weirdest idea ever. I was like, "I am rich!" I went from having $2,000 living with my parents to buying my own house, like, hello! And I'm not hip-hop, so I can't be throwing money around thinking that's gonna work. But Dre's the man.

I was running on a treadmill in London and the lyrics just came to my brain. It was the perspective of me living the dream. I put that vision into the verses: I had a mansion in London, Harajuku Girls and these things that actually happened in my life. That was the only way I could embrace the song’s [Fiddler on the Roof interpolation], which was perfect for me, because I love musicals. I later did that with "Wind It Up" and The Sound of Music.

I worked with David LaChapelle on the video, who's absolutely crazy. [laughs] That video was a nightmare to make. People were partying in the trailer with Pamela Anderson, and I cried on set. It was a wild time. I had such an idea of what I wanted it to be, and what he came up with was so elaborate. There was really no concept, so I didn't know if it was gonna turn out good. It ended up being great, but it was such a crazy day.

3. Hollaback Girl

I think it was the perfect song to represent what I wanted to achieve musically. It made sense that it was with Pharrell [Williams], because he was the first person who I worked with outside of No Doubt for "Hella Good." I really wanted No Doubt to work with new people on [2001's] Rock Steady, because [2000's] Return to Saturn took so long to make. Looking back, you can see on Rock Steady that [the music] started going in the direction of where I went with L.A.M.B. Jive is a dumb word to use, but I really jived with Pharrell. He's from Virginia Beach and mainly did hip-hop, and I'm in this ska band from Anaheim. But we were so similar: we love Japanese culture and both have clothing lines.

I was being bullied by someone and was being called a cheerleader, which was a bad thing! Growing up, that was not cool. I thought I was the opposite of that. I told Pharrell we should write a song about that. He always had this little keyboard that he writes everything on and he programs stuff into it. He goes, "This beat?" And he played "Hollaback Girl.” I was like, "What the fuck are you doing? You had that in there all these hours and you never played that until now? Why didn't you play that the first time I walked in here?" [laughs]

He's such a weirdo! We were talking about different cheers we remembered from high school. Then he goes, "I'm gonna leave!" He always does that during sessions and never takes me with him. He makes me write the rest of the song. When he came back, we did the Tom Cruise thing where we jumped on the couches. Like, holy s--t, we made the perfect song. It was such a culture collision between us. We called Jimmy and got some Cristal -- that's what everyone was drinking at the time -- and called everyone to the studio. But they didn't even put it out until the third single! I can't believe that's my song.

4. Cool

I wrote that with Dallas Austin. He was one of the dopest songwriters at the time -- he'd done some really big stuff with TLC. It was all so outside my genre of music. I thought, "What am I doing?" You have to understand, I lived at my parents' house until I was 26. My boyfriend and best friend [Kanal] was in my band, so he took care of me. So I was very sheltered. So for me to fly to Atlanta by myself and go to this gigantic hip-hop guy's studio was a big deal for me, and it was scary. Dallas was a really sweet guy. He took me to his mansion that was like a spaceship, this crazy bachelor pad. This was around the time Usher's "Yeah!" came out. Atlanta was super hot and so different from what I experienced in Anaheim.

Dallas already had the chords written, and it just said something about "being cool" on it. I loved the song because it reminded me of early Madonna and that time period of my youth. For me, it's very hard to finish something that's already been started. But I'm really proud of that song. Lyrically, it has a different perspective on love. Typically you don't talk about still being friends with somebody that you loved so much who broke your heart. It made so much sense at the time. Not only did I have a lot of guilt doing the record outside of No Doubt because it felt like I was cheating on them, but I also knew I needed to do it. It was always so weird to have been in a band with the person I was pretty much obsessed with and worshipped. Then he broke up with me and we became friends. It was a very complicated situation with Tony. At that point, I just got married, too, so there was a lot of stuff in my brain.

I absolutely loved David LaChapelle by the way, but for this video I wanted to work with Sophie Muller again. We went to Lake Como, Italy -- that was the time when we had big budgets. That was a $7,000 lace front wig that I had made. Back in those days, they gave you money to do stuff. [laughs]

5. Bubble Pop Electric feat. Andre 3000

It's so fun to talk about all the geniuses I got to work with. It makes me sad that I don't hear [new music] from Andre 3000. I'm such a huge fan of OutKast. When you watch someone be a genius in front of you, you get super intimidated. There's so many levels. Not only are you super talented, but you're also handsome and from a completely different culture. It was just an amazing experience, and I don't really want to take any credit for that song. I sat next to Andre and watched him write it.

We were two people that probably shouldn't be in the room together -- it was unexpected. “Bubble Pop Electric” was one of those things where I didn't understand what was happening because it was that out there! He was really supportive of my vocals, and wanted me to do these really weird harmonies he made up. I can't believe I got to meet Andre, let alone work with him.

6. Luxurious

Tony is the one that turned me on to a lot of music. He went to Anaheim High School, which was more Latino and gangster, and he loved dance music. That's what he would listen to when I met him at 16. When I was working on the record, I told him, "C'mon, we can write songs like that! Like ['80s freestyle artist] Debbie Deb!" He was learning how to be a producer and use Pro Tools -- all that was happening while we were writing. So it was us being naive and inexperienced trying to write music that we loved growing up.

The song was written already before the sample [of The Isley Brothers' "Between The Sheets"] was put in. We brought the song to Nellee Hooper, who worked with us on Rock Steady. He was the coolest European producer at the moment. Tony didn't want to put the sample in there because there's all these legal things that happen where you have to give away the publishing. But it seemed too perfect that it fit in like that.

7. Harajuku Girls

I got to work with Jimmy Jam & Terry Lewis on this song. What business did I have working with them? Every time I would go into the next writing session, I would already have my songs. So it was a snowball effect where everybody would start to get on board. It fueled their fire to keep up with whatever the last song they heard was. That song doesn't follow any rules. It has four billion different melodies. I would freestyle it and they'd piece it all together.

When it first came out, I think people understood that it was an artistic and literal bow down to a culture that I was a superfan of. This album was like a dream. I went in thinking I'm going to make something that could never be possible -- me doing a dance record -- come true. It was almost like a joke, because I thought that could never happen to me. So it was my fantasy. When the Harajuku Girls came out, it was like, you're not even real, you're a dream. It wasn't like, "You're not real because you're Asian." Are you kidding me? That would be horrifying!

So when people asked me about it during radio interviews, I told them this was all a concept and we were having fun. By the way, the girls were cast to be dancers -- that's all. We went to Nobu in London and we talked about the concept of the record and I showed them my style bible. Judging by their own personalities, I called them "Love," "Angel," "Music" and "Baby." It was like we were creating a group together.

I wanted to write a song that talked about my love for Harajuku. When you're from Anaheim and never traveled outside of your city until you're 21 years old, it was really crazy to go to Japan. My dad went there a lot because he worked with Yamaha motorcycles, so I had a fascination from a young age. When I got there and saw how fashion-obsessed they were, I thought they were my people, because my style was so unique. I get a little defensive when people [call it culture appropriation], because if we didn't allow each other to share our cultures, what would we be? You take pride in your culture and have traditions, and then you share them for new things to be created.

8. Crash

Tony and I were very much trying to do this freestyle-inspired song. We loved that kind of music, and he's the one who introduced me to it. We were all about trying to have fun while making it. Lyrically it wasn't so serious, but when I look back it does have a lot of meaning to it. And it was like the first time I used words like "baby." [laughs] But that's what they did in dance music. It's actually very hard to write music like that. I'm proud of this song too, it's very cool.

9. The Real Thing

I wrote this one with Linda [Perry]. There's not that much to say about it, but it was us trying to go in that New Order lane. And the band members [Bernard Sumner and Peter Hook] actually play on the song. Linda really wanted to do what I wanted and was all about praising me. It was beautiful because I could tell her, "I really love this song and I want to sound like this so bad." I would come in the next day and she would've done it. She would do the music part, I'd write the lyrics and we'd write the melodies together. I'm very specific about lyrics -- that's the one thing I wouldn't really collaborate on.

10. Serious

This was another one I did with Tony. I'm also really proud of this song because we didn't have these big-shot talented people in the room. It was just me and him who were just kids that grew up together. We loved music so much and [were] learning as we went and was trying to imitate things we thought were cool. I remember he had this tiny little studio in the back room of the house's main quarters -- you could barely fit in it. We would just sit on the floor and write these songs.

11. Danger Zone

I was trying to do this Dale Bozzio from [Los Angeles new wave band] Missing Persons vibe. Even though this record was supposed to be fun, I can't even listen to that song. There was so much tragedy going on in my life -- it was crazy. To be able to go back now and think about what was to come after that and what a horrible relationship I was in, it's crazy to me. It's weird to know that at the time, [those problems] were right there in front of me. When I went back to listen to some of the words, I was like, "I was saying it the whole time!" And there was nothing I could do.

12. Long Way To Go feat. Andre 3000

I think this song is a masterpiece. Andre wrote this entire record by hand. You can have a concept or feeling, but the record basically took on a journey of everybody that I worked with. He wanted to make that statement [about interracial relationships]. Especially with the fact that we were working together, too. I don't know if people judged him for working with me or he was thinking of that idea of different races coming together. One of my favorite lines in the song is "What color is love?" It's such a beautiful song.

If people ever missed that one, they should go back and listen because it's incredible. It's such a serious subject. The record was supposed to be this joke in a way, but it turned out to be an artistic statement that I never thought I would get to make. It was this deep, triumphant love record, masked in this fun music.