In attempting to define the "ecology" of human development, the term's history and connotations are discussed. The ecological approach requires that the person, the environment, and the relations between them be conceptualized in terms of systems, and subsystems within systems. The experimental situation is not limited to being unidirectional and dyadic, allowing only first-order effects. Two or more environmental settings can and should be included, and these environments should be studied and described along with the subject. An ecology of human development must be concerned not only with the developing child, but also with the developing ecology; that is, changes both in the micro- and macrostructures which envelop the child and those in his immediate environment. Finally, the author urges a reversal of usual experimental procedure, beginning the experiment by trying to change one of the environmental elements in order to get some idea of the delicate balance between the developing organism and its surroundings. (Author/BW)