The study of complex systems through agent based modelling present opportunities for marketing researchers to develop time and space explanations of interactions that occur in the marketplace and determine emergent phenomena, such as the adoption of new technology or successful business networks. The use of simulations and the ideas of complex systems though may appear baffling to many and the acceptance of simulations, especially agent based models has a long way to go given concerns about the validity and realism of many models. In this special issue we aim to present a number of papers which show a wide range of applications of agent based models to study business environments and consumer behaviour. There are also theoretical and methodological papers dealing with this new research paradigm. The validation of simulation models both by competing programs and with real world data is discussed in this special issue.