Biological Processes in Living Systems is the fourth and final volume of the Toward a Theoretical Biology series. It contains essays that deal in detail with particular biological processes: morphogenesis of pattern, the development of neuronal networks, evolutionary processes, and others. The main thrust of this volume brings relevance to the general underlying nature of living systems. Faced with trying to understand how the complexity of molecular microstates leads to the relative simplicity of phenome structures, Waddington-on behalf of his colleagues-stresses on the structure of language as a paradigm for a theory of general biology. This is language in an imperative mood: a set of symbols, organized by some form of generative grammar, making possible the conveyance of commands for action to produce effects on the surroundings of the emitting and the receiving entities. Biology, he writes, is concerned with algorithm and program. Among the contributions in this volume are: The Riemann-Hugoniot Catastrophe and van der Waals Equation, David H. Fowler; Differential Equations for the Heartbeat and Nerve Impulse, E. Christopher Zeeman; Structuralism and Biology, Rene Thom; The Concept of Positional Information and Pattern Formation, Lewis Wolpert; Pattern Formation in Fibroblast Cultures, Tom Elsdale; Form and Information, C. H. Waddington; Organizational Principles for Theoretical Neurophysiology, Michael A. Arbib; Stochastic Models of Neuroelectric Activity, Jack D. Cowan. Biological Processes in Living Systems is a pioneering volume by recognized leaders in an ever-growing field.