In this introductory chapter we provide a concise overview of the state of the art of mathematical models of the freight transport system, focussing mainly on areas where it deviates from passenger transport models. We introduce a conceptual model of the freight transport system that includes production, consumption and trade, as well as inventory and transport logistics. A brief explanation is given of the disciplinary background and the state of the art of freight modelling in these areas, and the different theoretical perspectives behind freight transport models are highlighted. Finally we provide an introduction to the different chapters of the book. The chapters largely follow the conceptual model introduced here and include overarching topics on data issues, simplified models and application for policy.