Agalloch (/ˈæɡəlɒx/) is an American extreme metal band from Portland, Oregon. Formed in 1995 by frontman John Haughm, they released five full-length albums, four EPs, two singles, one split single, two demos, four compilation albums and one live video album. They announced their disbandment in May 2016, but reunited in 2023.

Named after the resinous wood of the agarwood (Aquilaria agallocha), Agalloch began as the creation of Haughm and keyboardist Shane Breyer. In early 1996, the duo began composing material. Guitarist Don Anderson joined the band that summer to further refine the songs, which were recorded that autumn for release as the band's first demo tape, From Which of This Oak. This recording displayed a significant black metal influence and included material which would later appear on subsequent albums in one form or another. Shortly after the recording, bassist Jason William Walton was added to the lineup.

In 1998, the trio recorded a new demo tape, Promo 1998, solely for labels. It caught the attention of The End Records, who offered them a contract, resulting in the 1999 release of their debut full-length album, Pale Folklore. Reworking several earlier demo tracks, the album featured less of a black metal influence, more neofolk elements and neoclassical interludes. After the recording was completed, Breyer departed the band due to a lack of interest in music.

After a hiatus, the band released an EP of unreleased material from 1998 to 2001 titled Of Stone, Wind, and Pillor, revealing more neoclassical and experimental elements. The EP also included a cover of "Kneel to the Cross" by neofolk band Sol Invictus that would later be released on Sol Lucet Omnibus, French label Cynerfierrd's tribute compilation to Sol Invictus.

During the 2001 to early 2002 period, Agalloch recorded The Mantle, featuring more of a post-rock influence, namely the work of Godspeed You! Black Emperor, with tracks In The Shadow Of Our Pale Companion and You Were But A Ghost In My Arms prominently displaying the hybrid of black metal/post-rock influence found on the record. This album marked a change in media attention for Agalloch, landing them interviews with mainstream magazines.

Following the release of The Mantle, Agalloch played their first show on March 6, 2003 in Portland, followed by a few additional shows in March and a US West Coast tour in May.

Two subsequent records, the Tomorrow Will Never Come 7" single (issued by The End's Infinite Vinyl Series in 2003) and The Grey (released by Vendlus Records in 2004), showcased an even more experimental side of Agalloch, featuring remixed and reworked versions of songs from The Mantle as well as a new post-rock-influenced title track on the B-side of Tomorrow Will Never Come. Agalloch performed a series of shows on the North American East Coast in 2004.

A nature-themed split 10" picture disc single with the Finnish band Nest was also released in 2004, showcasing a collaborative, neofolk effort by Agalloch on the A-side. The Nest track, a more electronic, percussion-heavy effort, included vocal and guitar contributions by Haughm and Anderson.