Straight edge (sometimes abbreviated sXe or signified by XXX or X) is a subculture of hardcore punk whose adherents refrain from using alcohol, tobacco, and other recreational drugs, and in some cases even from promiscuous sex, in reaction to the excesses of punk subculture. The term straight edge was adopted from the 1981 song "Straight Edge" by the hardcore punk band Minor Threat.

A typical designation of straight edge is a black X on the back of the hand, as this kind of marking has been used in punk venues to denote underage guests who were not to be served alcohol at the bar.