The purpose of this paper is to present a state-of-the-art survey of the subject of system dynamics. This will include a brief historical review and an outline of the methodology, which is increasingly being recognised as having two separate phases. These are the qualitative diagram construction/analysis phase and the quantitative simulation phase. The purpose of the former is to develop a perspective on the system under study, covering its processes, information, organisational structure and strategies. Alternative types of system dynamics diagrams will be presented for this phase, the generic building blocks of these explored and some aspects of qualitative analysis discussed. The purpose of the simulation phase is to translate the system diagrams into behaviour over time. A summary of the steps of simulation analysis will be given and attention drawn to new thinking in sub-techniques and developments in simulation languages.