Jay W. Forrester (1918 - 2016) was a pioneering American computer engineer and systems scientist. He was a professor at MIT and later at MIT Sloan School of Management. Forrester is credited with being one of the inventors of magnetic core memory, the creator of the first computer animation, and the father of the field of System Dynamics - a computer-aided approach for strategy and policy design.In Principles of Systems, Professor Forrester explains the basic principles behind system behavior. He introduces the concepts of structure and dynamic behavior that were first introduced in his prior books, Industrial Dynamics (1961) and Urban Dynamics (1971). Due to the general nature and wide applicability of the principles discussed, this book has been adopted by numerous colleges and universities as an introduction to teaching System Dynamics in many multidisciplinary courses on urban, environmental, corporate, and other complex social systems. The accompanying workbook also allows students to gauge their learning throughout the book. The book serves on its own as well as being a complement to other books on the nature of social systems.Professor Forrester wrote many widely known papers in engineering and management. In addition, his other books laid the foundations for the application of System Dynamics to the behavior of complex social systems: Industrial Dynamics, reprinted in 1999, originally published in 1961 Urban Dynamics, 1969 World Dynamics, Second Edition 1973, originally published in 1971 Collected Papers of Jay W. Forrester, 1975These are available for purchase at www.systemdynamics.org.