The book examines theories (models) of how systems (those of humans, nature, and combined humannatural systems) function, and attempts to understand those theories and how they can help researchers develop effective institutions and policies for environmental management. The fundamental question this book asks is whether or not it is possible to get beyond seeing environment as a sub-component of social systems, and society as a sub-component of ecological systems, that is, to understand human-environment interactions as their own unique system. After examining the similarities and differences among human and natural systems, as well as the means by which they can be accounted for in theories and models, the book examines five efforts to describe human-natural systems. The point of these efforts is to provide the means of learning about those systems so that they can be managed adaptively. The final section of the book uses case studies to examine the application of integrated theories/models to the real world.