This study looks into heavy metal harmony from the point of view of music theory and analysis; the main focal point is the era that has been called "classic" or "traditional". This era ranges roughly from the late 1960s to the mid-1980s, including bands such as Black Sabbath, Deep Purple, Led Zeppelin, Judas Priest, and Iron Maiden. The study illuminates characteristics - from the elementary to the complex - which may be considered central to the harmonic language of heavy metal in that time period. Meanwhile, the applicability of traditional theories and methods of music analysis are discussed in the context of this music.