Part I: Preliminaries: Chapter 1. Introduction.- Chapter 2. Uncertainty and complexity: towards model-based demography.- Part II: Elements of the modelling process.- Chapter 3. Principles and state of the art of agent-based migration modelling.- Chapter 4. Building a knowledge base for the model.- Chapter 5. Uncertainty quantification, model calibration and sensitivity.- Chapter 6. The boundaries of cognition and decision making.- Chapter 7. Agent-based modelling and simulation with domain-specific languages.- Part III: Model results, applications, and reflections.- Chapter 8. Towards more realistic models.- Chapter 9. Bayesian model-based approach: impact on science and policy.- Chapter 10. Open science, replicability, and transparency in modelling.- Chapter 11. Conclusions: towards a Bayesian modelling process.