A simple and flexible activity-based simulation for Belgium Johan Barthélemy and Philippe Toint naXys Technical Report naXys-10-2013 29 October 2013 Abstract. The VirtualBelgium project aims at developing understanding of the evolution of the Belgian population using agent-based simulations and considering various aspects of this evolution such as demographics, residential choices, activity patterns, mobility, etc. This simulation is based on a validated synthetic population consisting of approximately 10,000,000 individuals and 4,350,000 households localized in the 589 municipalities of Belgium. The work presented in this paper focuses only on the mobility behaviour, simulated using an activity-based approach in which the travel demand is derived from the activities performed by the individuals. The proposed model is distribution based and requires only minimal information, but is designed for easily taking advantage of any additional network-related data available. The proposed activity-based has been applied on the Belgian synthetic population. The quality of the agent behaviour is discussed using statistical criteria extracted from the literature and it is shown that VirtualBelgium produces satisfactory results.