"The paper presents a phenomenological approach in which metamorphosis is introduced as an interactional concept. For a traditional psychology of development the basic assumption is that of a constant environment as the objective context for an individual changing from child through adulthood to old age, adapting to the environment in accordance with his or her changing abilities and skills. If applied to this positivist conception, "metamorphosis" would merely mean the experiential and behavioral changes from child to adolescent to adult - an impoverished notion of the really ongoing changes in and through the life-cycle. This positivist conception is contrasted with a phenomenological and contextualist approach. Based on the concept of an intentional environment, i.e. the world as it is experienced and acted upon, the focus is on the different meanings and functions that differentiate a baby's world from a child's, an adolescent's, an adult's, a senior's environment. As a necessary addition the idea of gendered environments is introduced, which permits of distinguishing between boys' and 'jirls', between men's and women's environments. In the phenomenological framework "metamorphosis" refers to the change of lived worlds through different stages of the life-cycle. "Lived world" is used here as an interactional construct meaning both the environment as experienced (i.e. perceived, thought of, felt, remembered) and as acted upon and hence modified by the actor. While it is difficult (and, within a paper, impossible) to describe metamorphic developments of whole age-related environments, it is possible to exemplify such changes for certain essential features of person-environment interactions. Hence, in its second part this paper will focus on developmental changes in the experience of ranges, borders, and barriers of activity as constitutive elements of socio-physical space. Mainly with respect to these features it will be demonstrated that with developmentally increasing and (in old age) decreasing ranges of activity the meanings and functions of physical as well as social barriers and borders change. They change, for instance, from insurmountable obstacles and impassable limits to means-to-ends, even challenges in themselves, and, later in age, "back" again to inhibiting environmental features. Data from developmental and gerontological research in home and urban settings corroborate this interactional conception of metamorphosis."