After a demo and the EP Mosquito Control were recorded by the original lineup, Mereschuk was replaced by Jay Randall in 1999, who joined the group alongside guitarist Michael Gallagher.

Isis disbanded in June 2010, just before the release of a split EP with the Melvins, reforming only once in 2018 as Celestial for a one-off show to pay tribute to Caleb Scofield.

In 1999, Michael Gallagher (formerly of Cast Iron Hike) and Jay Randall (now of Agoraphobic Nosebleed) joined the band, working on Red Sea (1999).

After releasing their full-length debut entitled Celestial (2000) and its sister EP, SGNL›05 (2001, on Neurot Recordings), Isis gained national underground attention in the metal/hardcore scene through tours with Cave In and Neurosis.

[4] The entire band were avid fans of Melvins, so their label – Mike Patton's Ipecac Recordings – was instantly put forward as an ideal candidate.

[4] Whereas Celestial was still deeply rooted in heavy metal and hardcore, 2002's follow-up, Oceanic, saw the band acquire new characteristics comparable to post-rock and ambient music, significantly aiding in the birth of the genre of post-metal in what many saw as a logical progression.

[8] It was at the time their most successful release, receiving album-of-the-year accolades from Rock Sound and Terrorizer in 2002,[9] In late 2003, Isis relocated to Los Angeles.

[10] The distinctive tone of material since and including Oceanic had a noticeable impact on avant-garde metal,[11] helping develop the sound of several contemporaries; Cult of Luna, Pelican, Tides, Rosetta, and Russian Circles all cite Isis as an influence.

The album featured another remix by Justin Broadrick, who has supported Isis on tours with his band, Jesu, which is signed to Hydra Head Records.

[20] Also in September 2006, a collaboration with Aereogramme entitled In the Fishtank 14 was released as part of a project of Dutch label Konkurrent in which two artists are given two days' studio time to write and record their work.

The record sees the band again evolving in a manner similar to Oceanic and Panopticon, this time adding new elements of electronics, song structure, drumming complexity, and vocal techniques.

It sees the emergence of a more melodic sound than before, and leanings away from previous "drone" inclinations and towards more traditional metal elements, predominantly in the heavier sections.

Turner has stated that "We never imagined that Isis would become as successful or as popular as it has",[23] and confesses: "[Fans] taking a deeply personal interest in who I am, it fucking freaks me out.

[25] The album's sound continued Isis' legacy of lengthy songwriting, and presents a slight departure from the soft-loud dynamics which characterised previous releases.

[29] Extensive touring followed the album's release, taking in headlining shows across the United States, Europe, Japan and Australia with bands including Baroness, Big Business, Cave In and Melvins.

[39] In 2011 Jeff Caxide, Aaron Harris and Bryant Clifford Meyer sought out to continue creating music together and formed Palms featuring Chino Moreno of Deftones on vocals and guitar.

[43] The band reunited for a one-off show on October 13, 2018 (under the name "Celestial") at a benefit for the family of Caleb Scofield, the Cave In bassist who died in a road accident seven months earlier.

[44][45] Turner cites Swans, Melvins, Tool, Godflesh, and Neurosis as influences to Isis' sound, saying "those bands laid the groundwork for us [...] we're part of a recognizable lineage.

Revolver critic Dan Epstein noted that "though [Isis were] originally lumped in with the hardcore and doom-metal scenes, the band has long since transcended the musical boundaries of those genres".

"[57] Circa 2005, both Turner and Gallagher used Gibson Les Paul guitars with Mesa Boogie V-Twin preamp and a Mackie power amp.

[2][48] Books such as Don Quixote, House of Leaves, Labyrinths and the philosophies of Jeremy Bentham have all played a role in shaping the themes of Isis' releases.

[59] Turner has complained that "metal in general has long been unjustly maligned as solely the province of knuckle-dragging meatheads [...] That said, there's never been a group of musicians like there is now, who are helping to advance the form.

Turner has stated: "we wanted to have albums that weren't just grab-bags of songs but rather a cohesive experience from beginning to end, from the music to the lyrics to the layout of the record.

Turner does not explicitly acknowledge an "overtly feminine theme"; however, he does state: "I just think it's interesting to include that as part of what we do, simply because metal, especially, is considered to be this very male-oriented, testosterone-driven art form, and I feel like it's important to recognize the other side of our nature.

"[2] After constantly explaining concepts and story outlines to interviewers and fans, Turner chose to keep the thematic basis of In the Absence of Truth quiet.