5 Seconds of Summer, often shortened to 5SOS (pronounced "five sauce"), are an Australian pop rock band formed in Sydney in 2011. The group consists of lead vocalist and rhythm guitarist Luke Hemmings, lead guitarist Michael Clifford, bassist Calum Hood, and drummer Ashton Irwin. Originally beginning their career as YouTube celebrities, they rose to international fame while touring with English-Irish boy band One Direction on their Take Me Home Tour. Since 2014, 5 Seconds of Summer have sold more than 10 million albums, sold over 2 million concert tickets worldwide, and have attained more than 7 billion streams of their songs on music streaming services, making them one of the most successful Australian musical acts in history.

In early 2014, the band released "She Looks So Perfect" which topped the charts in four countries. Their self-titled debut album was released in 2014, peaking at number one in 11 countries. The band released their second album Sounds Good Feels Good in 2015, topping the charts in 8 countries. The band's third album Youngblood, released in 2018, was yet another commercial success and became their third number one album in their home country. In the US, 5 Seconds of Summer became the first Australian act to achieve three number one albums on the Billboard 200 album chart. They also became the first band (not vocal group) to have their first three full-length albums debut at the top in the US. The album's single, "Youngblood" is the fourth highest selling Australian single of the 2010s decade and is the eleventh best-selling single in Australian history, selling over five million adjusted copies worldwide within the first six months of its release. With the release of "Youngblood", 5 Seconds of Summer became the first Australian act in 13 years to top the ARIA year-end chart and remain the second longest stint at number one in ARIA chart history. In 2020, the band released their fourth studio album Calm. The album was a commercial success, receiving positive reviews from critics, charting in more than 25 countries on multiple charts, peaking in the 10 top on 17 charts and debuting atop the charts in 4 countries. With Calm earning the band their fourth consecutive number one in their home country, 5 Seconds of Summer became the second Australian band in history to have their first four full-length studio albums debut at number one on the ARIA albums chart.

All singles from the band's four studio albums have charted in multiple countries, received multiple official sale certifications, and have been featured in numerous weekly and year-end charts, as well as making appearances on decade-end charts. The band has received numerous accolades and awards, including being honored with the prestigious APRA Outstanding International Achievement Award in 2019, being placed on Billboard's Top Artists of the 2010s chart, which lists the most popular and successful artists of the 2010–2019 decade and being credited in the exclusive APRA AMCOS 1,000,000,000 List in 2020. As of mid-2020, the band's estimated net worth is approximately US$81 million.