f(x) (Hangul: 에프엑스) is a four member South Korean girl group formed by SM Entertainment in 2009. The name is a play on the mathematical notation for function, with "f" signifying "flower" and "x" representing the female's double X chromosome. The group made their debut on September 1, 2009 with release of a digital single "라차타 (LA chA TA)". The quartet consists of 宋茜 (Victoria), 엠버 (Amber), 루나 (Luna), and 크리스탈 (Krystal).

Krystal was first spotted by SM Entertainment in 2000, which earned her a small role in a short segment of Shinhwa's "Wedding March" music video. Former member 설리 (Sulli) first debuted as a child actress in 2005 when she was selected to play young Princess Sun-hwa in the SBS television drama, The Ballad of Seo-dong. In 2006, SM Entertainment recruited Luna after seeing her performing on SBS's television program, "Truth Game". In September 2007, SM Entertainment recruited Victoria Song. A month later, Amber was cast from an audition in Los Angeles, California.

SM first released a teaser preview of the group via YouTube on August 24, introducing them as "Asia's Pop Dance Group." For five days, SM individually released information through news portals and posted pictures of each member on SM Town's official website, starting with Korean member Sulli on August 26, Taiwanese-American member Amber on August 27, Korean-American member Krystal on August 28, Korean member Luna on August 29, and lastly the Chinese member Victoria on August 30.

On September 1, the group's first single "라차타 (LA chA TA)" was digitally released. Following their first performance at the Samseong-dong Fashion Center on September 2, the music video was screened and released online the next day. The group's first broadcast performance of "La Cha Ta" was held at MBC's music show Show! Music Core on September 5.

On October 7, the group also released the electro-pop version of the digital single, "Chocolate Love", alongside their label mate Girls' Generation. The single was released for the promotion of the 4th edition Blacklabel series of LG CYON phone, LG Chocolate (BL40).

On November 9, f(x) released their first single album Chu~♡.

On May 4, f(x) released their first mini-album NU ABO. The lead single "NU ABO" topped online music portal charts Monkey3, Dosirak and Bugs. The song also made it to the Gaon Chart weekly number-one singles. The music video for the song was released on May 6. The group made their live comebacks on KBS's Music Bank on May 7, MBC's Music Core on May 8 and SBS's Inkigayo on May 9. On July 17, the group started performing their next promotional single, "Mr. Boogie".They had their first performance for the song on MBC's Music Core.

It was announced by SM Entertainment that Amber returned from USA after a long leave since June 2010 and that f(x) are planning to release a studio album in February 2011. f(x) finally released their first album PINOCCHIO on April 20, 2011. The album's lead single "(피노키오) Danger" immediately went to #1 and stayed at the top of various online charts such as Melon. On April 29, f(x) received their first k-chart award on Music Bank. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.