Abstract
After an exposure of basic concepts for the definition of stages of life, such as maturation, the influence of critical life events, the role of developmental tasks, and socialization of some prescientific models of life’s phases are outlined. Already the prescientific models show what functions scientific life stage and life phase models have, e.g., deviations from a “normal state” attract a desire to intervene, whether through education, counseling, or psychotherapy. Then some modern scientific life-cycle orientated models for phases and stages of life are described. These models consider individual development—as a lifelong project—embedded in cultural processes. This leads to a “broader concept of development” where individual differences and differential changes come into the focus. Lifetime development is an interplay between society, history, culture, and biology with important practical, political, economic, ethical implications.