"On the basis of her almost 30 years of research experience on Environmental Psychology. to understand people's interaction with their physical environment, the author discusses the great change that has occurred in the last 20 years in the concept of "physical environment", affecting researchers, designers and decision makers. This change is due to the effect of the "ecological/global revolution". which began in natural sciences, and received strong support from various International and United Nations Organizations and Programmes (such the MAB-UNESCO Program) since the 70s'. A milestone in this process was the 1992 Rio (Brasil) United Nations Conference on "Environment and Development", which identified "sustainable development" _ and thus "environmental sustainability"_ as the main human goal and challenge for the 2lth Century and approved the "Agenda 21" as the main indication of action in this direction. Two major "revolutionary perspectives" can be distinguished within this "ecological revolution", because of the different ways they have in considering the relationship between human behavior and environment and thus the role of human behavior for a sustainable environment. Both perspectives should be involved in order to move towards sustainable development.The implications of the introduction of the concept of "sustainable environment" for researchers, designers, decision makers and users are discussed, pointing out how the adoption of this new concept imposes a much wider spatial and temporal perspective on all of these environmental actors, in the consideration of the physical features of the environment, ranging from the local to the global and from current to future generations' needs. It is proposed that most of today's "shifting balances" discussed at the present IAPS 15 Conference could be related to the impact of these changes, not yet sufficiently assimilated by this Association, on the study of people-physical environment interactions."