2NE1's first song was "Lollipop", digitally released on March 27, 2009. The song was created for LG Cyon to promote their Lollipop phone, and it was a joint release with Big Bang; the commercial/music video debuted on March 28, 2009. Although it was not a promoted single (as it was an advertisement song, there were problems with network chart eligibility), "Lollipop" proved to be a strong chart hit, going to #1 on various online charts and topping music television network M.Net's online chart for four weeks in a row. It was also profiled in Perez Hilton's blog. However, questions were raised about the group's future, as the song's success was attributed to the popularity of Big Bang.
On April 30, Yang Hyun-suk revealed that 2NE1's debut song would be a hip hop/reggae song, and that it would be digitally released on May 6, 2009. Titled "Fire", the song was fully written and produced by 1TYM's Teddy Park. Teasers of the song were released on their official website at the beginning of May, with a 20-second clip released on May 1.
On its first day, it recorded 50,000 sales in pre-orders. Their debut was a success on the Korean charts, and it headed straight to number 1 for its debut week, in which It sold 13,675 copies.
YG stated that the EP had already reached the 80,000 sales mark within 2 weeks, which is impressive since 2NE1 is only a rookie.
 By the end of 2009 2NE1 sold approximately 100,000 copies. It continued to show strong sales by charting on the 2010 year end chart for Gaon, selling an additional 40,949 copies. Total sales for the release are believed to be 140,949 copies.
"Lollipop", written and produced by Teddy Park, was digitally released on March 27, 2009. Despite not being promoted traditionally by both groups, the song nonetheless was a major success in South Korea; giving the girls a number #1 song before their debut.
"Fire" was the official single from the album. Released in May, the song became a hit on various on- and offline charts. It was released as planned on May 6, with two versions of the music video — a "space" version and a "street" version — released the same day. The videos received over one million views in a day; the viewcount then increased to two million.
"I Don't Care" was the third single from 2NE1, co-produced by Teddy and YG's newly signed rising producer Kush. Soon after its release, the music video was also profiled in Perez Hilton's blog who declared them his "favorite" Korean girl-group. The single proved to be their most successful endeavor and went on to win Song of the Year at the 11th Mnet Asian Music Awards, making them the first girl group and group in general to win the esteemed award the same year of debut, and the second rookie to win after Bigbang for "Lies" (2007).
The group's first performance of the song was on May 17, 2009, on SBS's Inkigayo. beginning the group's activities. Their first performance was also included in Perez Hilton's blog once again, showing his interest towards the group.
Both the song and the group have been very popular online, with the song topping M.Net's online chart and the group's name becoming a top search term. The group was also rewarded with three Cyworld Digital Music Awards, with both "Lollipop" and "Fire" winning "Song of the Month" awards and the group winning "Rookie of the Month" for May 2009. They received their first Mutizen award during their fourth stage performance in SBS Inkigayo (Popular Song) on June 14, 2009. They received their second Mutizen award on SBS Inkigayo (Popular Song) on June 21, 2009.
For closed the promotion of the first mini album was released the song "In The Club" as first promotional single of the album.