Hard rock is a form of rock and roll music that finds its closest roots in early 1960s garage rock. AC/DC, The Stooges, MC5, Jimi Hendrix and Deep Purple are renowned examples of hard rock. Van Halen's music (until David Lee Roth's departure in 1985) perhaps best exemplifies the energy of the genre. Hard rock achieved maximum popularity between 1969 and 1985, and soon thereafter gave way to hair metal.

Hard Rock is often loosely defined, and is primarily of use in describing radio station formats. There is often significant crossover with heavy metal music, but a few distinctions are worth noting: Hard Rock typically features major key song construction, as opposed to heavy metal, which is often minor key oriented. There is a heavy reliance on the pentatonic scale for most elements of song construction, and fifths (power chords) are often substituted for traditional chords. Chord progressions are commonly associated to 1-4-5 degrees of the scale, as in rock and roll.

Hard Rock lyrics are typically not as "dark" as heavy metal lyrics, and are often sexual in content.

Hard Rock is typified by a bright, trebly overdrive distortion effect on the guitars, lending to its overall sound. Drums can range from 100-150 Beats Per Minute, with 120 BPM being typical. Bass is usually warm sounding.

The guitar solo is very important part of a hard rock song, and leads to the credibility of the song just as much as the lyrics and vocal melodies do. Songs are generally hook laden, and consist of:

1. an intro
2. verse
3. chorus
4. verse
5. chorus
6. solo
7. chorus
8. an ending

There is much room for variation, and repetition of verses and choruses.

Jazz, Blues, and rock & roll were the roots of hard rock.

Punk rock, Gothic rock, industrial music, heavy metal, funk, and fusion also claim these roots, but branch off at different points, eliminating elements that are considered unnecessary, and adding elements to typify their genre. Interestingly, death metal and industrial music also incorporate a march rhythm.

The term "hard rock" is also used as an umbrella term for genres such as Punk, Gothic rock, Industrial, and Metal, in order to distinguish them from softer, more radio friendly Pop music. Obviously, the double use of "hard rock" has led to confusion in the past.