This article considers how genre is treated in metal fan communities and metal scholarship. In identifying shortcomings in the existing literature with regard to genre definitions, it argues that musical characteristics should be the primary defining characteristics of metal subgenres. To this end, this article posits both a taxonomy for classifying metal genres and a model for analysing their characteristics. This model consists of five characteristics - pitch, timbre, form, rhythm and aesthetics - which, when combined, can elucidate the specific musical and extra-musical elements that comprise metal's various subgenres. This provides a framework through which metal musicology and other scholarship can develop a common background and work towards concrete definitions of metal subgenres.