This chapter has seen us examining the origins of systems thinking in disciplines as diverse as philosophy biology, sociology, management and organization theory, control engineering, and the physical sciences. Even this is not complete. A study of psychology, for example, would have seen us having to give attention to Gestalt theory — our tendency to create order in the world around us by seeing it in terms of wholes. We have also witnessed the birth of systems thinking per se and considered some candidates for a general theory of systems — general system theory itself, autopoiesis, cybernetics, chaos and complexity theory. Once established, systems thinking began to feed its insights back both into the disciplines that produced it and disciplines that, lacking a developed theoretical framework, felt that they could make use of systems ideas. In the latter category would come geography (e.g. Chorley and Kennedy, 1971; Chapman, 1977; Bennett and Chorley, 1978)and political science (e.g. Deutsch, 1963; Easton, 1973; and Yon Pil Rhee, 1999). Essentially, with some gaps acknowledged, we now understand the main features of systems thinking as it developed in the disciplines and as a transdiscipline in its own right. We are at the point where it is possible to turn to the use that can be made of systems ideas. In the 1940s systems thinking began to give rise to specific methodologies for intervening in the real world to solve practical problems. It is this –applied systems thinking— that is the subject of the next chapter.