Billie Eilish Pirate Baird O'Connell ( EYE-lish; born December 18, 2001) is an American singer and songwriter. She first gained public attention in 2015 with her debut single "Ocean Eyes", written and produced by her brother Finneas O'Connell, with whom she collaborates on music and live shows. In 2017, she released her debut extended play (EP), Don't Smile at Me. Commercially successful, it reached the top 15 of record charts in numerous countries, including the US, UK, Canada, 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 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. Her subsequent singles "Everything I Wanted", "My Future", "Therefore I Am", and "Your Power" peaked in the top 10 in the US and UK. Her second studio album, Happier Than Ever (2021), topped the charts in 25 countries. She 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.

Eilish has received multiple accolades, including nine Grammy Awards, two American Music Awards, twenty Guinness World Records, seven MTV Video Music Awards, three Brit Awards, two Golden Globe Awards, and two Academy Awards. She is the second artist in Grammy history to win all four general field categories—Record of the Year, Album of the Year, Song of the Year, as well as 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 Recording Industry Association of America (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, gender equality, and animal rights.