Summary: The Second Edition features expanded coverage of progress in systems science, focusing on the field's overall structure and its components - including systems terms and concepts, complexity, measurements, and principles. The text offers a framework for understanding the underlying theory of systems science to assist decision makers in resolving a wide range of real-world problems in their fields. Revised and expanded chapters cover the origins and evolution of systems science and incorporate different perspectives on complexity. Various approaches to problem solving in the natural and social sciences are described, including the systematic view model and model decomposition. The book also presents clear and coherent accounts of systems intervention, critical systems thinking, and quantification of systems science. Philosophical issues in systems science are comprehensively covered, with discussion on such topics as ontology, epistemology, and methodology. Other features of the Second Edition include: case studies focusing on the application of the viable system model, methodology application, and theory building; a list of thought-provoking questions for each chapter to assist educators; an introduction to critical systems thinking; a chapter on model decomposition; and various approaches to problem solving, including systems intervention.