ABBA ( AB-ə, Swedish: [ˈâbːa], formerly named Björn & Benny, Agnetha & Anni-Frid or Björn & Benny, Agnetha & Frida) are a Swedish supergroup formed in Stockholm in 1972 by Agnetha Fältskog, Björn Ulvaeus, Benny Andersson, and Anni-Frid Lyngstad. The group's name is an acronym of the first letters of their first names arranged as a palindrome. One of the most popular and successful musical groups of all time, they are one of the best-selling music acts in the history of popular music, topping the charts worldwide from 1974 to 1982, and in 2022.

In 1974, ABBA were Sweden's first winner of the Eurovision Song Contest with the song "Waterloo", which in 2005 was chosen as the best song in the competition's history as part of the 50th anniversary celebration of the contest. During the band's main active years, it consisted of two married couples: Fältskog and Ulvaeus, and Lyngstad and Andersson. With the increase of their popularity, their personal lives suffered, which eventually resulted in the collapse of both marriages. The relationship changes were reflected in the group's music, with later compositions featuring darker and more introspective lyrics. After ABBA separated in December 1982, Andersson and Ulvaeus continued their success writing music for multiple audiences including stage, musicals and movies, while Fältskog and Lyngstad pursued solo careers.

Ten years after the group broke up, a compilation, ABBA Gold, was released, becoming a worldwide best-seller. In 1999, ABBA's music was adapted into Mamma Mia!, a stage musical that toured worldwide and, as of April 2022, is still in the top-ten longest running productions on both Broadway (closed in 2015) and the West End (still running). A film of the same name, released in 2008, became the highest-grossing film in the United Kingdom that year. A sequel, Mamma Mia! Here We Go Again, was released in 2018.

In 2016, the group reunited and started working on a digital avatar concert tour. Newly recorded songs were announced in 2018. Voyage, their first new album in 40 years, was released on 5 November 2021 to positive critical reviews and strong sales in numerous countries. ABBA Voyage, a concert residency featuring ABBA as virtual avatars, opened in May 2022 in London.

ABBA are among the best-selling music artists in history, with record sales estimated to be between 150 million to 385 million sold worldwide and the group were ranked 3rd best-selling singles artists in the United Kingdom with a total of 11.3 million singles sold by 3 November 2012. ABBA were the first group from a non-English-speaking country to achieve consistent success in the charts of English-speaking countries, including the United Kingdom, Australia, United States, Republic of Ireland, Canada, New Zealand and South Africa. They are the best-selling Swedish band of all time and the best-selling band originating in continental Europe. ABBA had eight consecutive number-one albums in the UK. The group also enjoyed significant success in Latin America and recorded a collection of their hit songs in Spanish. ABBA were inducted into the Vocal Group Hall of Fame in 2002. The group were inducted into the Rock and Roll Hall of Fame in 2010, the first recording artists to receive this honour from outside an Anglophonic country. In 2015, their song "Dancing Queen" was inducted into the Recording Academy's Grammy Hall of Fame.