15 years ago, the group's second CD sold 2.4 million copies in its first week of release – a record that has yet to be topped.

IN APRIL 2000, 'N SYNC WAS ON TOP of the world. The members of the group – Lance Bass, then 20; J.C. Chasez, 23; Joey Fatone, 23; Chris Kirkpatrick, 28; and future prince of pop Justin Timberlake, 19 – were steadily building in popularity since their first hit, "I Want You Back," debuted on the Pop Songs chart in January 1998.

But, things were about to get much bigger. RCA Records (through a production deal with Louis "Lou" Pearlman's Trans Continental Group) released the boy band's self-titled debut in March 1998, and although it debuted at a rather lowly No. 82 on the Billboard 200, it hit the top 10 four months later and remained there until the following March. A 1998 Christmas album also peaked in the top 10.

'N Sync's highly anticipated follow-up, No Strings Attached, was set for a pre-Christmas 1999 release until the group signed a label deal with Jive Records, which triggered a $150 million breach-of-contract lawsuit by RCA's then-parent BMG and Trans Continental. The band struck a deal in December that enabled it to stick with Jive, and No Strings was released on March 21, 2000.

Pent-up demand for the album and its smash lead single, "Bye Bye Bye" – No. 1 for 10 weeks on Pop Songs – led to a blockbuster bow on the April 8, 2000-dated Billboard 200. According to Nielsen Music, the album sold 2.4 million copies, the single-largest sales week for an album since Nielsen began tracking data in 1991. The record still stands.

Although the act – which went on hiatus in the mid-2000s after releasing a final album, Celebrity, in 2001 – did regroup to perform at the 2013 MTV Video Music Awards, it has no further reunion plans.

A version of this article first appeared in the April 11 issue of Billboard magazine.