The counterculture of the 1960s was an anti-establishment cultural phenomenon and political movement that developed in the Western world during the mid-20th century. It began in the early 1960s, and continued through the early 1970s. It is often synonymous with cultural liberalism and with the various social changes of the decade. The effects of the movement have been ongoing to the present day. The aggregate movement gained momentum as the civil rights movement in the United States had made significant progress, such as the Voting Rights Act of 1965, and with the intensification of the Vietnam War that same year, it became revolutionary to some. As the movement progressed, widespread social tensions also developed concerning other issues, and tended to flow along generational lines regarding respect for the individual, human sexuality, women's rights, traditional modes of authority, rights of people of color, end of racial segregation, experimentation with psychoactive drugs, and differing interpretations of the American Dream. Many key movements related to these issues were born or advanced within the counterculture of the 1960s.

A revolutionary is a person who either participates in, or advocates for, a revolution. The term revolutionary can also be used as an adjective to describe something producing a major and sudden impact on society.