Mastodon has been described as a heavy metal band, along with more specific genres such as progressive metal, sludge metal, alternative metal, stoner rock, psychedelic metal, experimental metal, and groove metal. James Christopher Monger of AllMusic describes Mastodon as "one of the more notable new wave of American heavy metal acts, a genre spawned in the mid-'90s" and says that "Mastodon's innovative, lyrically astute blend of progressive metal, grindcore, and hardcore helped position the band as one of the preeminent metal acts of the early 21st century."