Billie Eilish Pirate Baird O'Connell (/ˈaɪlɪʃ/ EYE-lish; born December 18, 2001) is an American singer-songwriter and musician. Eilish first gained public attention in 2015 with her debut single "Ocean Eyes", written and produced by her brother Finneas O'Connell. In 2017, she released her debut EP, Don't Smile at Me, which was commercially successful, in various countries, including the US, UK, and Australia.

Eilish's debut studio album, When We All Fall Asleep, Where Do We Go? (2019), debuted atop the US Billboard 200 and UK Albums Chart and was one of the year's best-selling albums. Its single "Bad Guy" became the first by an artist born in the 21st century to top the US Billboard Hot 100 and be certified Diamond by the Recording Industry Association of America (RIAA). The next year, Eilish performed the theme song "No Time to Die" for the James Bond film No Time to Die, which topped the UK Singles Chart and won the Academy Award for Best Original Song in 2022.

Eilish's second studio album, Happier Than Ever (2021), topped the charts in multiple countries. Its singles "My Future", "Therefore I Am", "Happier Than Ever", and "Your Power", each peaked within the top ten in the US and UK. She co-wrote and performed "What Was I Made For?" for the fantasy film Barbie (2023), which became her second number-one single in the UK and earned her a second Academy Award. Her third album, Hit Me Hard and Soft (2024), was met with critical acclaim and spawned the US top-five singles "Lunch" and "Birds of a Feather", with the latter becoming her first number-one on the Billboard Global 200.

Her accolades include two Academy Awards, nine Grammy Awards, nine American Music Awards, twenty Guinness World Records, eight MTV Video Music Awards, four Brit Awards, and two Golden Globe Awards. She is the second artist in Grammy history (after Christopher Cross) to win all four general field categories—Record of the Year, Album of the Year, Song of the Year, and Best New Artist—in the same year. Eilish is also the first person born in the 21st century to win an Academy Award and the youngest ever two-time winner. She was featured on Time magazine's inaugural Time 100 Next list in 2019 and the Time 100 in 2021. According to the RIAA and Billboard, Eilish is the 26th-highest-certified digital singles artist and one of the most successful artists of the 2010s. She was honored as one of the BBC 100 Women in December 2022. Eilish has a history of political activism, focusing on climate change awareness, women's reproductive rights, and gender equality.

Billie Eilish Pirate Baird O'Connell was born in Los Angeles, California, on December 18, 2001. She is the daughter of actress and teacher Maggie Baird and actor Patrick O'Connell, both of whom are also musicians and work on Eilish's tours. Eilish is of Irish and Scottish descent. Her middle name, Eilish, was chosen by her parents while watching a documentary about Irish conjoined twins Katie and Eilish Holton and was originally meant to be her first name, while Pirate was to have been her middle name. After her grandfather William Baird died while her mother was pregnant, her parents decided to name her Billie, after him. She grew up in Los Angeles's Highland Park neighborhood.

Eilish and her older brother Finneas were homeschooled by Baird, a decision their parents made to spend time with them and give them the freedom to pursue their interests. Baird taught Eilish and Finneas the basics of songwriting. Eilish said her brother and mother inspired her to get into music. Their parents encouraged the siblings to express themselves and explore whatever they wanted, including art, dancing, and acting.

Eilish started playing the ukulele at age six. She performed at talent shows and joined the Los Angeles Children's Chorus at age eight. She wrote her first "real" song at age 11 for her mother's songwriting class. The song is about the zombie apocalypse, inspired by the television series The Walking Dead, from which she took script lines and episode titles. Eilish took some acting auditions, which she disliked, but she enjoyed recording background dialogue for crowd scenes and worked on the films Diary of a Wimpy Kid, Ramona and Beezus, and the X-Men series. Eilish also took dance classes until 2016, when a growth plate injury ended her dance career and she focused on recording music.

In 2015, 13-year-old Eilish began working on songs with her brother Finneas, who had been writing and producing for several years and had his own band. The first songs they recorded together were called "She's Broken" and "Fingers Crossed", the former written by Finneas and the latter by Eilish. "We recorded them and put them out on SoundCloud, just for fun", she recalled.