Hardline is a subculture that has its roots in the vegan straight edge hardcore punk scene. It is commonly seen as a more extreme version of straight edge, with influences from deep ecology philosophy. From its outset, hardline adherents put out statements and literature pushing a biocentric view of the world, which advocated for veganism, animal rights, pro-life, anti-homosexuality, and a much more militant version of the straight edge philosophy, which advocates for a no alcohol, no drugs, no tobacco lifestyle. The hardline worldview has been accused by critics as ecoauthoritarian. Hardline co-founder Sean Muttaqi adamantly rejected racism and fascism.

Straight edge is a subculture of hardcore punk whose adherents refrain from using alcohol, tobacco and recreational drugs in reaction to the punk subculture's excesses. Some adherents refrain from engaging in casual sex, follow a vegetarian or vegan diet and do not consume caffeine or prescription drugs. The term "straight edge" was adopted from the 1981 song "Straight Edge" by the hardcore punk band Minor Threat.