At today's iPhone 6 and Apple Watch launch, U2 made history by delivering their new album Songs of Innocence to 500 million iTunes users for free. You can play any selection from the track list and hear that this record is one of the rock band's most personal yet.

In an interview with Rolling Stone, Bono was candid about the people who made a mark on the album in both a literal (Danger MouseRyan Tedder) and figurative (The Clash, The Ramones, Bono's mother) sense. Here are 5 insights on the album gleaned from that interview.

1) The personal connection wasn't an accident, and they wanted to go further with Songs of Innocence in that respect than they have with previous efforts.
"We wanted to make a very personal album," Bono told RS. "Let's try to figure out why we wanted to be in a band, the relationships around the band, our friendships, our lovers, our family. The whole album is first journeys — first journeys geographically, spiritually, sexually. And that's hard. But we went there."

2) U2 enlisted big-name producers (Danger Mouse, OneRepublic's Ryan Tedder, longtime collaborator Flood and Adele producer Paul Epworth) for a reason, and it paid off. 
"I think having them around really helped. Some of the music out there now that people call pop, it's not pop – it's just truly great. And we wanted to have the discipline of the Beatles or the Stones in the '60s, when you had real songs. There's nowhere to hide in them: clear thoughts, clear melodies."

3) Songs of Innocence's first single is "The Miracle (of Joey Ramone)," named for the rocker who lit the match of Bono's musical being (even if he "sang like a girl"). 
"I found my voice through Joey Ramone because I wasn't the obvious punk-rock singer, or even rock singer. I sang like a girl — which I'm into now, but when I was 17 or 18, I wasn't sure. And I heard Joey Ramone, who sang like a girl, and that was my way in."

4) The song "This Is Where You Can Reach Me Now" is more than just a stylistic nod to The Clash.
"After we saw the Clash, it was a sort of blueprint for U2. We knew we couldn't possibly hope to be as cool, and that's proven to be true, but we did think we could get behind a sort of social justice agenda."

5) Bono wrote "Iris (Hold Me Close)" about his mother, who tragically died at his grandfather's funeral when he was a child. 
"Forty years ago, my mother fell at her own father's funeral, and I never spoke with her again. Rage always follows grief, and I had a lot of it, and I still have, but I channeled it into music and I still do. I have very few memories of my mother, and I put a few of them in a song called 'Iris.'"