Billie Joe Armstrong (born February 17, 1972 in Rodeo, California) is the songwriter, lead vocalist and guitarist for punk rock band Green Day. Armstrong was the youngest of six kids and lived in Rodeo, California. His father was a truck driver who died of cancer when Armstrong was ten. His mother was a waitress at Rod's Hickory Pit, which Billie and fellow bandmate Mike Dirnt also ended up working at in their teen years. He insists that his name be spelled with an 'ie' at the end of Billie, because that is how his mother wrote it on his birth certificate. According to the liner notes in 1,039/Smoothed Out Slappy Hours, "Billie's mom spelled his name wrong on his birth certificate 'cuz she was on drugs". He is the only member of Green Day who uses his real name, while Mike Dirnt (born Mike Pritchard) uses half of his real name.

Right before Armstrong's father died from cancer, he gave his son his first guitar, which Billie Joe nicknamed "Blue". It was a Fernandes Stratocaster copy and to this day he still uses replicas of the guitar. "Blue" has since become his trademark guitar because of its duct tape and sticker covered appearance. "Blue" was used in some of their most popular music videos including "Basket Case" and "Brain Stew/Jaded". Other instruments Armstrong can play include the piano, drums, harmonica and the mandolin. The first song he wrote was called "Why Do You Want Him" and was written in 1986, when he was 14 years of age. (His mom was dating someone he did not like at the time.) The song appears on Green Day's debut album on Lookout Records, 39/Smooth.

During his stay in school he was nicknamed "Two Dollar Bill", because he was supplying the school with joints for two dollars. In 1988, Billie Joe formed a band called Sweet Children with childhood friend, Mike Dirnt, and Al Sobrante (born John K). They changed their name to "Green Day" in March 1989, just before the release of their first EP, 1,000 Hours, on Lookout Records. The name Green Day comes from a slang expression for a day of pot smoking. In 1990 Sobrante left Green Day for college and was replaced by Tré Cool (born Frank Edwin Wright III), who appears on Green Day's second album, Kerplunk.

He and his wife Adrienne are co-founders and part owners of the independent label Adeline Records, and he has a side band called Pinhead Gunpowder which is on Lookout Records. He has two sons. Joseph Marcicano; born in March 1995, and Jakob Danger; born September 1998. Billie and Adrienne (vocalist and guitarist of all girl punk/emo band "I Love Jimmy") were married July 2, 1994 in Billie's backyard, the next day they learned she was pregnant. Billie now lives very happily with his wife Adrienne and children Joey and Jackub.

He stated that he is bisexual in an interview in The Advocate, January 24, 1995