Environmental design is a new term, which refers to deliberate structuring of human environments to allow specific patterns of experience and behavior. The concern of human biology with this emerging field arises, in part, from an understanding that the growth and differentiation of brain cells are affected both by the structure of experience, and by the time in the course of development during which particular experiences occur. This article discusses how environmental design involves structuring of human environments in a manner that allows optimal growth and expression of human behaviors. The contributions from biology to environmental design are crucial insofar as they provide a groundwork in the understanding of human behavior essential to the rational design of man's environment.