Altar is a collaborative album by Japanese experimental music group Boris and American drone metal band Sunn O))), released on October 31, 2006 through Southern Lord Records (SUNN62).

Japanese cult band Boris have had several Japan-only releases, until now. The title track is over one hour long. A bonus track 'Dronedevil 2' has been added for a total of 72 minutes. Beside pure heavy riff-droning bombast, boris add a unique ambience to all they touch, which explains their collaborations with Merzbow and Keiji Haino. Standard jewel case. 2001 release.