Barker’s ecological psychology gives environmental structure an empirical grammar through the concept of the behaviour setting. A setting is not merely a location in which conduct happens, but a recurrent organisation of people, activities, objects, temporal sequences and normative expectations whose elements display a degree of interdependence. The work’s iconic contribution is to treat everyday environments as patterned units that can be observed without reducing them either to individual psychology or to abstract social structure. Methodologically, Barker privileges extended observation, ecological description and the study of naturally occurring situations. This operation makes the environment legible as an active organisation of possibilities and constraints. The importance of the behaviour setting extends beyond psychology because it offers a model for analysing institutions, platforms and other organised situations as configurations that stabilise particular forms of participation. Barker therefore bridges environmental psychology with institutional and infrastructural analysis through a rigorous account of situated regularity.