Rock music is a genre of popular music that originated in the United States as "rock and roll" in the late 1940s and early 1950s, developing into a range of styles from the mid-1960s, primarily in the United States and United Kingdom. It has its roots in rock and roll, a style that drew from the black musical genres of blues and rhythm and blues, as well as from country music. Rock also drew strongly from genres such as electric blues and folk, and incorporated influences from jazz and other styles. Rock is typically centered on the electric guitar, usually as part of a rock group with electric bass guitar, drums, and one or more singers.

Usually, rock is song-based music with a ⁴
₄ time signature and using a verse–chorus form; however, the genre has become extremely diverse. Like pop music, lyrics often stress romantic love but also address a wide variety of other themes that are frequently social or political. Rock was the most popular genre of music in the U.S. and much of the western world from the 1950s up to the 2010s.

Rock musicians in the mid-1960s began to advance the album ahead of the single as the dominant form of recorded music expression and consumption, with the Beatles at the forefront of this development. Their contributions lent the genre a cultural legitimacy in the mainstream and initiated a rock-informed album era in the music industry for the next several decades. By the late 1960s "classic rock" period, a few distinct rock music subgenres had emerged, including hybrids like blues rock, folk rock, country rock, southern rock, raga rock, and jazz rock, which contributed to the development of psychedelic rock, influenced by the countercultural psychedelic and hippie scene. New genres that emerged included progressive rock, which extended artistic elements, heavy metal, which emphasized an aggressive thick sound, and glam rock, which highlighted showmanship and visual style. In the second half of the 1970s, punk rock reacted by producing stripped-down, energetic social and political critiques. Punk was an influence in the 1980s on new wave, post-punk and eventually alternative rock.

From the 1990s, alternative rock began to dominate rock music and break into the mainstream in the form of grunge, Britpop, and indie rock. Further subgenres have since emerged, including pop-punk, electronic rock, rap rock, and rap metal. Some movements were conscious attempts to revisit rock's history, including the garage rock and post-punk revival in the 2000s. Since the 2010s, rock has lost its position as the pre-eminent popular music genre in world culture, but remains commercially successful. The increased influence of hip-hop and electronic dance music can be seen in rock music, notably in the techno-pop scene of the early 2010s and the pop-punk-hip-hop revival of the 2020s.

Rock has also embodied and served as the vehicle for cultural and social movements, leading to major subcultures including mods and rockers in the U.K., the hippie movement and the wider western counterculture movement that spread out from San Francisco in the U.S. in the 1960s, the latter of which continues to this day. Similarly, 1970s punk culture spawned the goth, punk, and emo subcultures. Inheriting the folk tradition of the protest song, rock music has been associated with political activism, as well as changes in social attitudes to race, sex, and drug use, and is often seen as an expression of youth revolt against adult conformity. At the same time, it has been commercially highly successful, leading to accusations of selling out.

The sound of rock is traditionally centered on the amplified electric guitar, which emerged in its modern form in the 1950s with the popularity of rock and roll. It was also greatly influenced by the sounds of electric blues guitarists. The sound of an electric guitar in rock music is typically supported by an electric bass guitar, which pioneered jazz music in the same era, and by percussion produced from a drum kit that combines drums and cymbals. This trio of instruments has often been complemented by the inclusion of other instruments, particularly keyboards such as the piano, the Hammond organ, and the synthesizer. The basic rock instrumentation was derived from the basic electric blues band instrumentation (prominent lead guitar, second chordal instrument, bass, and drums). A group of musicians performing rock music is termed as a rock band or a rock group. Furthermore, it typically consists of between three (the power trio) and five members. Classically, a rock band takes the form of a quartet whose members cover one or more roles, including vocalist, lead guitarist, rhythm guitarist, bass guitarist, drummer, and often keyboard player or another instrumentalist.

Rock music is traditionally built on a foundation of simple syncopated rhythms in a ⁴
₄ meter, with a repetitive snare drum back beat on beats two and four. Melodies often originate from older musical modes such as the Dorian and Mixolydian, as well as major and minor modes. Harmonies range from the common triad to parallel perfect fourths and fifths and dissonant harmonic progressions. Since the late 1950s, and particularly from the mid-1960s onwards, rock music often used the verse–chorus structure derived from blues and folk music, but there has been considerable variation from this model. Critics have stressed the eclecticism and stylistic diversity of rock. Because of its complex history and its tendency to borrow from other musical and cultural forms, it has been argued that "it is impossible to bind rock music to a rigidly delineated musical definition." In 1981, music journalist Robert Christgau said, "the best rock jolts folk-art virtues—directness, utility, natural audience—into the present with shots of modern technology".

Rock and roll was conceived as an outlet for adolescent yearnings ... To make rock and roll is also an ideal way to explore intersections of sex, love, violence, and fun, to broadcast the delights and limitations of the regional, and to deal with the depredations and benefits of mass culture itself.