This thesis highlights the uses of agent-based models (ABMs) in social systems, ranging from simplified testing grounds for bottom-up hypotheses to trustworthy, policy-ready tools. Throughout the course of the thesis the different models will exemplify how multi-scale heterogeneity can be woven into ABMs and stress-tested “in silico” before considering real-world implementation of the modelled phenomena. The thesis is structured as a “journey” across four social settings, progressively increasing in realism and scale.