Based on a workshop held at the Santa Fe Institute in June, 1990, this book explores structure in organismsboth physical and dynamicaland presents the current status of the search for natural pathways, principles of organization, and the theory of design for organisms. Topics discussed include dynamical systems analysis; the pathways of evolution; development, physiology, and functional morphology; and the principles of dynamical change in connectivity within the networks of processes.The aim of the workshop was to seek principles of organization in organisms and a theory that could generate those principles, as Newtonian mechanics generates Kepler's laws of planetary motion. The object of the theory is to explain patterns of structure in living or past organisms, or patterns to be expected in future organisms. The book proposes principles of organization that are independent of time scale and level of organization, and that make predictions about structure without recourse to micro-level details. Among them are principles of coordination, evolution to the edge of chaos, the matching of processes to constraints, and the evolution of higher-level processes as a way to surmount resource limitations. These general principles, which may be characteristic of any evolving complex system, may then be used in conjunction with properties of the specific materials and processes in organisms to understand biological structure.