In the black metal subculture, authenticity is a central concept. While there are ample academic studies devoted to authenticity in hip hop, rock, country, punk, and other music genres, black metal authenticity remains relatively under-researched. This manuscript discusses how black metal fans construct authenticity. In-depth interviews with Dutch black metal fans reveal that they define authenticity along four highly interrelated dimensions: sincerity, commerciality, country of origin, and extremeness. While these dimensions are highly similar to those found in other music genres, our respondents’ constructions of authenticity are far from predictable. More specifically, they are much more complex and flexible than they might appear to outsiders to the subculture. We argue that this complexity is strongly related to the central role invocations of authenticity play in the drawing of boundaries around the subculture, as they ensure that authenticity cannot be easily staged but rather requires a profound investment in the subculture.