1. Introduction. Part Overviews. 2. Orientation and Structure. 3. Relevant Social Theory. 4. Origins in the Disciplines. 5. Applied Systems Thinking. Part Systems Approaches. 6. The Functionalist Systems Approach. 7. The Interpretive Systems Approach. 8. The Emancipatory Systems Approach. 9. The Postmodern Systems Approach. Part Critical Systems Thinking. 10. The Origins of Critical Systems Thinking. 11. Contemporary Critical Systems Thinking and Practice. 12. Critical Systems Three Illustrative Case Studies. 13. Conclusion.