The chronosystem is a concept in Bronfenbrenners ecological systems theory that refers to the role of time in shaping an individuals development. It considers how and when major events occur and how the timing of these events can influence a persons life. The chronosystem comprises both normative life transitions, such as graduating from school, marriage, birth of a child, and non-normative life transitions, such as an accident, winning a lottery, a parental divorce. It also includes broader historical events and cultural changes that can shape the experiences and developmental outcomes of individuals across generations.

The chronosystem is the outermost level in Bronfenbrenners 5-tiered model of child development called the ecological systems model. Each level in the model is represented by a circle, with the entire model taking the appearance of a series of 5 concentric circles moving outwards, with the child at its center. The radial distance of the circle from the center is proportional to the degree of immediate influence the system/level has on the development of the individual.

In summary, the chronosystem is a concept in Bronfenbrenners ecological systems theory that considers the role of time in shaping an individuals development. It comprises both normative and non-normative life transitions, broader historical events, and cultural changes that can shape the experiences and developmental outcomes of individuals across generations.