The “green book†twenty years on: A new look at the research program of Isard and Liossatos's “spatial dynamics and optimal space time development†**This note was originally prepared for the North American Meetings of the Regional Science Association International, Montreal, Quebec, Canada, November 11–14, 1999, in honor of Walter Isard's 80th birthday. The author would like to thank editor Jean Claude Thill and two anonymous referees for helpful comments and constructive criticisms

The publication in 1979 of Isard and Liossatos's Spatial Dynamics and Optimal Space Time Development marked the culmination of a progression of papers in which the authors explored parallels between processes modeled in theoretical physics and the spatial development of social systems. While providing a rigorous, incisive and exhaustive treatment of the subject, the book has begotten little secondary scholarship. This research note revisits the research program of what the senior author called his “green book†, assesses it from the present perspective, and considers how it might be continued in the light of recent theoretical, methodological and computational developments.