The Strauss–Howe generational theory, devised by William Strauss and Neil Howe, describes a theorized recurring generation cycle in American history and Western history. According to the theory, historical events are associated with recurring generational personas (archetypes). Each generational persona unleashes a new era lasting around 20–25 years, in which a new social, political, and economic climate (mood) exists. They are part of a larger cyclical "saeculum". The theory states that a crisis recurs in American history after every saeculum, which is followed by a recovery (high). During this recovery, institutions and communitarian values are strong. Ultimately, succeeding generational archetypes attack and weaken institutions in the name of autonomy and individualism, which eventually creates a tumultuous political environment that ripens conditions for another crisis.

A generation is all of the people born and living at about the same time, regarded collectively. It also is "the average period, generally considered to be about 20–⁠30 years, during which children are born and grow up, become adults, and begin to have children." In kinship, generation is a structural term, designating the parent–child relationship. In biology, generation also means biogenesis, reproduction, and procreation.