Jay W. Forrester has shown that computer simulation indicates that the intuitive models usually invoked to deal with planning contingencies lead to basically erroneous results. This is because the real world systems, of which the web of socio-economic-environmental organization (WSEEO) is now, perhaps, of major significance to the future of man, are multi-loop, nonlinear feedback systems whose structures run counter to the intuitive, simplistic models usually invoked for studying and dealing with our global, environmental problems. In addition, planning and policymaking also frequently ignore “system breaks” that have rendered the models invoked obsolescent and non-isomorphic to the segment of the real world with which a planner is concerned. Planning models are needed that will change with time, in recognition of the system breaks that are occurring, sometimes over relatively short periods. These system breaks often lead to unstable parameters in the more simplistic models employed. The important task in planning and policymaking is to capture accurately the structures of the complex systems for which we are trying to plan. In this sense the determination of the particular values of the parameters of our models is less important than the task of developing models that approximate the real-world structure with ever greater, structural precision. In the case of developmental, economic planning, we find that adding more of the existing types of technologies and manufacturing processes to the world's capital stock, through efforts to industrialize underdeveloped economies, increases the pollution and degradation of the world-wide WSEEO. This adds another pitfall to developmental planning which—if it is to escape contributing to pollution and degradation of the WSEEO—must avoid the conventional, currently existing capital-stock framework. Appropriate, developmental planning must try to develop technologies and modes of industrialization that reduce global pollution and ecological degradation and which, at the same time, minimize the amount of unrecycled waste poured into local regions of the planet's environment. In short, models for planning and policy-making must more and more be of the multi-loop, nonlinear type and must incorporate unconventional technologies and industrial processes not of the type that is commonly found in the West. Some of the basic objectives and requirements of such models for the planning and policy sciences are briefly suggested by the author.