The liner notes for the METAL ALLEGIANCE album read like a massive chunk of a heavy metal encyclopedia, with contributions from past and present members of MEGADETH, TESTAMENT, DREAM THEATER, LAMB OF GOD, SLAYER, EXODUS, MASTODON, PANTERA, TRIVIUM, KINGS X, HATEBREED, SEPULTURA, MACHINE HEAD, ANTHRAX, LACUNA COIL, THE DILLINGER ESCAPE PLAN, PERIPHERY, DEATH ANGEL, JUDAS PRIEST, ICED EARTH, and ARCH ENEMY. Live incarnations of METAL ALLEGIANCE have seen guest appearances from Geezer Butler (BLACK SABBATH), Phil Campbell and Mikkey Dee (MOTORHEAD), Wolfgang Van Halen (VAN HALEN), Steve Vai and Billy Sheehan.
As Troy Sanders (MASTODON) declared when he joined Metal Allegiance at the NAMM Convention in January 2015: "Holy Shit! I've been invited to the All-Star game!"