Girls' Generation (Korean: 소녀시대; RR: Sonyeo Sidae), also known as SNSD, is a South Korean girl group formed by SM Entertainment. The group is composed of eight members: Taeyeon, Sunny, Tiffany, Hyoyeon, Yuri, Sooyoung, Yoona, and Seohyun. Originally a nine-piece ensemble, member Jessica departed from the group in September 2014. Among the most influential girl groups in K-pop and a leading figure of the Korean Wave, Girls' Generation has earned numerous accolades and the honorific nickname "The Nation's Girl Group" in their home country.

Girls' Generation debuted on August 5, 2007, with the single "Into the New World" from their eponymous Korean album. The group rose to fame in 2009 with the single "Gee", which claimed the top spot on KBS's Music Bank for a record-breaking nine consecutive weeks and was Melon's most popular song of the 2000s decade. The group cemented their popularity in Asia with follow-up singles "Genie", "Oh!", and "Run Devil Run", which were released between mid-2009 and early 2010. Their second Korean studio album, Oh! (2010), won the Golden Disc award for Album of the Year (Disk Daesang), making the group the first and only female act to win the Album Daesang.

Girls' Generation ventured into the Japanese music scene in 2011 with their eponymous Japanese album, which became the first album by a non-Japanese girl group to be certified million by the RIAJ. The group's third Korean studio album, The Boys, was the best-selling album of 2011 in South Korea. An English version of the title track was released in an attempt to expand the group's endeavor to the global music scene. The group's fourth Korean studio album, I Got a Boy (2013), was supported by the title track, which won Video of the Year at the inaugural YouTube Music Awards. Girls' Generation continued to build upon their popularity with their fifth and sixth Korean studio albums, Lion Heart (2015) and Holiday Night (2017). Following a five-year hiatus to focus on their individual careers, they returned with their seventh Korean studio album Forever 1 (2022).

The group's signature musical styles are characterized as electropop and bubblegum pop, though their sound has varied widely, incorporating various genres including hip hop, R&B, and EDM. In 2017, Billboard honoured Girls' Generation as the "Top K-pop Girl Group of the Past Decade". They are the first Asian girl group to achieve five music videos with over 100 million views on YouTube with "Gee", "I Got a Boy", "The Boys", "Mr. Taxi", and "Oh!". In Japan, they became the first non-Japanese girl group to have three number-one albums on the Oricon Albums Chart, and their three Japanese concert tours attracted a record-breaking 550,000 spectators.

The group's Korean name is So-Nyeo Si-Dae (Korean: 소녀시대; Hanja: 少女時代; RR: Sonyeo Sidae), from the Sino-Korean root meaning "Generation of Girls"; they are also known as SoShi (소시) or SNSD, both of which are abbreviated forms of the group's Korean-language name. Because their name consists of Chinese roots, the group's name is similar in Chinese and Japanese: in Japan the group's name is pronounced as Shōjo Jidai (少女時代), and in Mandarin Chinese as Shàonǚ Shídài (simplified Chinese: 少女时代; traditional Chinese: 少女時代).

Prior to the group's debut, some of the members were already involved in the entertainment industry. Yoona had gone through about 200 auditions for music videos, dramas, and movies before becoming a singer for Girls' Generation. Sooyoung was exposed to the Japanese music scene as a member of a pop duo named Route 0, which disbanded one year after its debut in 2002.

The first member of the group to join SM Entertainment's training system was Jessica in 2000, after she and her sister, Krystal Jung, were scouted in a mall in South Korea during a family vacation. That same year, members Sooyoung and Hyoyeon were cast into S.M.'s training system through the 2000 S.M. Open Audition, in which Hyoyeon danced for her audition. Yuri was the next Girls' Generation member to become an S.M. trainee after coming second in the 2001 S.M. Youth Best Dancer competition. Yoona was cast the following year through the 2002 S.M. Saturday Open Casting Audition, where she sang and danced to her favorite singers, BoA and Britney Spears. Seohyun, the group's youngest member, was scouted in the subway by an S.M. scout; she then auditioned in 2003, singing children's songs.

The group's leader, Taeyeon, was cast in 2004 after winning first place in the S.M. Youth Singing Competition. That same year, member Tiffany auditioned at S.M.'s Starlight Casting System in Los Angeles, and joined the company in October 2004. The final member of the group to be added was Sunny, who had become an S.M. trainee in 1998 and trained for five years before moving to another company, Starworld. At Starworld, she trained to debut in a duo named Sugar, which never debuted. In 2007, on the recommendation of Korean-Japanese singer IconiQ, Sunny moved back to S.M. Entertainment and became a member of Girls' Generation.