Book excerpt: This book explores how transportation models can play a role in a changing transport planning and policy making context. Most models are rooted in decades of development work and are geared to offer value-free, academic and explicit knowledge to transport planning experts. However, planning practice has changed dramatically over the years, resulting in a less technical rational view on the use of such knowledge – especially so in early, strategy making phases. More and more complex policy goals, integration of a wide area of other policy domains, a wider, ever-changing and much more mixed group of planning participants and much more focus on ‘wicked problems’. The book maps how this influences the effectiveness of transport modelling exercises and explores several state-of-the-art implementations. This book was published as a special issue of Transport Reviews.