We present an electronic book titled “Simulation and Modelling of System Dynamics”, just recently published online by the International Environmental Modelling & Software Society (iEMSs), and authored by the late Peter Benyon.Simulation allows exploration of more complex models than can be analysed theoretically; it can be used where trials on the real world system would be too costly, time consuming or dangerous. This book provides for the needs of those undertaking simulation.The book aims at a wide readership using an informal style. The material varies from elementary to advanced and encourages selective browsing and reading, with a wide range of examples and chapter summaries to aid this choice.The material focuses on the need to formulate the models with the right structure and equations – in other words, it concentrates on system description rather than model solution. The importance of subsequent validation is indicated.The book is freely accessible and it is available online as a PDF file at: http://www.iemss.org/docs/books/ModSimSysDynA.pdf.