This symposium considers how people-environment theory might be grounded insocial science, ecological and design transdisciplinarity, thereby advancing corresponding research, education, policy and practice. Transdisciplinarity is compared with bounded territories of uni- and sub-disciplinarity, and clusters of multi-, pluri- or inter-disciplinarity in which separate aspects of a whole phenomenon are addressed. The symposium explores core (uni- and sub-disciplinary), contextual (multidisciplinary) and core-contextual (transdisciplinary) relationships between people and the physical environment, in keeping with the expressed aims of IAPS.