Heavy metal lyrics are the words used in songs by heavy metal artists. Given that there are many genres of heavy metal, it is difficult to make generalizations about the lyrics and lyrical themes. In 1989, two metal scholars wrote that heavy metal lyrics concentrate "on dark and depressing subject matter to an extent hitherto unprecedented” in any form of popular music.Jeffrey Arnett states that metal songs are "overwhelmingly dominated" by "ugly and unhappy" themes which express "no hope" for the future.Deena Weinstein has proposed one way to analyze metal song themes is loosely grouping them into two categories: the Dionysian theme (a reference to the Roman God of wine), which celebrates “sex, drugs and rock and roll”, partying, and enjoyment of life and the Chaotic theme, which involves dark subjects such as Hell, injustice, mayhem, carnage and death. Not all metal genres fall into Weinstein's two theme model; for example power metal's lyrical themes often focus on fantasy and mythology, camaraderie and hope, personal struggles and emotions, among other themes. Another exception is pop metal bands, which replaced “gloom and doom” themes with “positive, upbeat” songs about romantic love and relationships, part of their goal of appealing more to female listeners. In metal overall, the small number of metal songs about relationships are typically about unions that have “gone sour” long ago.
The thematic content of heavy metal lyrics has long been a target of criticism. According to Jon Pareles, "Heavy metal's main subject matter is simple and virtually universal. With grunts, moans and subliterary lyrics, it celebrates ... a party without limits ... [T]he bulk of the music is stylized and formulaic." Music critics have often deemed metal lyrics juvenile and banal, and others have objected to what they see as advocacy of misogyny and the occult. During the 1980s, the Parents Music Resource Center (PMRC) petitioned the U.S. Congress to regulate the popular music industry due to what the group asserted were objectionable lyrics, particularly those in heavy metal songs. The PMRC used music professor Joe Stuessy to testify against metal. Professor Stuessy alleged that heavy metal songs focus on violence, substance abuse, perversion, S&M, and Satanism. Robert Walser analyzed 88 metal songs' themes to determine if Professor Stuessy’s claims were valid. In Walser’s analysis, the dominant theme in the metal songs was “longing for intensity”; he found that the negative themes described by Stuessy and the PMRC were uncommon. Jeffrey Arnett analysed the lyrics from 115 metal songs: he found that the top three messages were "grim...themes" about violence, angst and protest.