Stage theory is a term used to describe the process of successive development, or the transition from one state of organisation to another. It is based on traditional cognitive development theories such as Jean Piaget's, suggesting that development proceeds through identifiable stages. It is used to understand the progression of disruptive events, both in terms of personal psychological transformation and in terms of the life-stages of cultures and societies. Importantly, a stage theory approach to development is not linear, but rather recognises that each stage is a necessary step for the subsequent development of an individual or a collective.

See also: spiral dynamics, systems theory, complex system, relationship