Hard rock is a sub-genre of rock music which has its earliest roots in mid-1960s garage and psychedelic rock and is considerably harder than conventional rock music. It is typified by a heavy use of distorted electric guitars, bass guitar, keyboards and drums.

Hard rock is strongly influenced by blues music; the most frequently used scale in hard rock is the pentatonic, which is a typical blues scale.[1] Unlike traditional rock and roll (which takes elements of the "old" blues), hard rock incorporates elements of "British blues", a style of blues played with more modern instruments such as electric guitars, drums, keyboards and electric bass. A notable departure from traditional blues forms is that hard rock is seldom restricted to the I, IV, and V chords prevalent in twelve or sixteen bar blues, but includes other chords, typically major chords rooted on tones of the minor scale.

The term "hard rock" is often applied to many styles of rock music, their only common feature being that they deviate from pop rock, though this is generally incorrect. Two such examples are punk rock and grunge. Punk rock uses a faster tempo, less melody, fewer riffs (often using barre chords), more aggression and anti-establishment lyrics.