So how did the Aussie punk-rockers – Luke Hemmings, Calum Hood, Michael Clifford and Ashton Irwin – get their start? Cowriters and producers John Feldmann, Jake Sinclair and Alex Gaskarth tell PEOPLE how their debut LP all came together.
Write a Hit in One DayIt reached No. 1 in five countries and the video has more than 80 million views, but there was never some elaborate plan or hours spent toiling over "She Looks So Perfect."
"I came up with it when I was in line buying underwear at American Apparel. And then I was like, 'That'll be perfect for these kids!' " L.A.-based writer-producer Sinclair, 29, says of the ubiquitous chorus he penned for 5SOS.
Sinclair met up with band members Irwin (drums, vocals) and Clifford (guitar, vocals), and the rest is Top 40 history.
"We finished writing it and produced it that day," says Sinclair, 29, who has worked with everyone from Taylor Swift and Fall Out Boy to Pink. "They're really positive and fun to have in the studio ... It was really easy."
Get a Musical MentorFeldmann has an eye for emerging artists. And the Red Bull Records writer-producer – he's worked with Ashlee Simpson, Good Charlotte and the Plain White T's, to name a few – was hooked when he first saw 5SOS perform.
They're a real band. That was my first impression," he says. "They're all really good at what they do. I was just blown away."
Noel Kessel / Newspix / Getty
"She would not leave Luke alone. She'd be slapping his butt and hanging on his leg," he says. "It may sound weird, but it's telling to me when you have that sort of charisma or energy that goes along with the frontman, which Luke kind of is."
Feldmann spent a lot of time with the guys and has watched them grow up in the spotlight, which he says they've handled with ease. "It hasn't changed since day one. They're still the same four guys. They're like brothers," he says. "They love each other and know where they came from."
Gain Approval From Another Punk-RockerWhen Feldmann found out the boys were All Time Low fans, he introduced them to the band's lead singer, Gaskarth, who became a writing partner on three of the LP's songs.
"They have a very similar dynamic to our band: Everybody gets along," Gaskarth says. "To see another group doing it a few years younger than us – it's really cool."
The rocker says there was never a dull moment during recording sessions. "Songwriting's a good time. We weren't taking ourselves too seriously ... If you're not laughing and having fun doing it, you're doing it wrong," says Gaskarth, who co-wrote "Kiss Me Kiss Me."
"Whenever we were strung out on a song or needed a minute to clear our minds, we'd play [ping-pong] like normal," he says. "But if you hit the ball off the table or lose a point, you play shirtless, and you have to let the person who scored on you rail the ball at your back."
The 5SOS guys tend to write in pairs, which Gaskarth says worked well. "Michael and Ashton are goofballs – they brought a ton of energy to the songs we wrote together," he says. Meanwhile, "Calum and Luke were kind of the quiet ones at first. Once we got going, they started to come out of their shells."
Now, Gaskarth says, the sky's the limit for the new group.
"They're such hard workers," he says, "and they're so dedicated to what they're doing that I don't see it slowing down for them."
For much more about the boys – and 145 fun photos! –, check out PEOPLE's special 5SOS issue, on stands now