Grand Declaration of War is the second full-length studio album by the Norwegian black metal band Mayhem, released by Season of Mist and Necropolis Records on 6 June 2000.

[5] In his book Mean Deviation: Four Decades of Progressive Heavy Metal, Jeff Wagner wrote that Grand Declaration of War features "a variety of vocal shadings to match the multi-layered music", between "A Time to Die", described by Wagner as "one minute and forty-eight seconds of black calculus", "A Bloodsword and a Colder Sun" offering "squishy electronic groove, so close to trip-hop that it instantly became the album's most controversial track" and the "mesmerizing ten-minute sprawling landscape of doom" "Completion in Science of Agony".

The album's "sonic clarity" was "a complete 180-degree turn" from the band's early "scuzzy 'necro' approach".

[1] Alex Henderson of AllMusic stated that the band "has outdone itself with the epic Grand Declaration of War, which could arguably be described as black metal's equivalent of Queensryche's Operation: Mindcrime".

[2] A remastered version of the album was released in December 2018; the original 'cold', 'sterile' production was swapped out for a more raw sound with the bass and drums made more prominent in the mix.