The chapter covers computational simulation methods in the social sciences with a particular focus on how they interrelate with online methods, in particular new kinds and amounts of data. After briefly covering system dynamics and microsimulation the chapter concentrates on agent-based modelling. Agent-based modelling is an individual based simulation method able to tackle different levels of aggregation (structure-agency), variability of individuals (heterogeneity) and spatial aspects of phenomena (spatiality). Problems of agent-based modelling are discussed, in particular the lack of appropriate data for model validation. Online research methods are discussed as a source of new kinds of data that might solve some of those problems.