Answer by taking a quote from the following article:

Interpol is an American rock band from New York City. Formed in 1997, the band's original line-up consisted of Paul Banks (vocals, rhythm guitar), Daniel Kessler (lead guitar, vocals), Carlos Dengler (bass guitar, keyboards) and Greg Drudy (drums, percussion). Drudy left the band in 2000 and was replaced by Sam Fogarino. In 2010, shortly after recording finished for the band's fourth album, Dengler left to pursue personal projects.

After self-releasing several EPs between 1998 and 2001, the band signed with Matador Records, a member of the independent Beggars Group, in early 2002. The first release, a self-titled EP containing re-recorded versions of "PDA" and "NYC" was released in June 2002. Turn On the Bright Lights was released on August 19, 2002. Recorded at Tarquin Studios in Bridgeport, Connecticut, the album's sound drew comparisons to post-punk groups of the early 1980s and late 1970s, particularly Joy Division, Echo and the Bunnymen and The Smiths. The record was a slow-building success, selling 300,000 copies by 2004.  The band regrouped in late 2003 to begin sessions for the follow-up album, again decamping to Tarquin Studios to record. The band released its second album Antics on September 27, 2004. The album sold 350,000 copies in its first four months of release. The record also saw the band earn its first UK Top 40 hits with "Slow Hands", "Evil" and "C'mere" charting at No. 36, No. 18 and No. 19, respectively. The album eventually reached gold status in the UK, and later in the US.  The band toured again after the release of the album, playing more dates than ever before and at bigger venues. The Antics tour stretched on for almost 18 months, including a number of shows playing as undercards for U2 and The Cure, and the band reported feelings of exhaustion to BBC Radio 1 DJ Zane Lowe at a concert in Sunderland. The band took three months off after touring finished. Whilst on the road, the band had also released the one-off track "Direction", written for the official soundtrack to HBO's Six Feet Under, Six Feet Under, Vol. 2: Everything Ends.

What was their best selling album?
its second album Antics