Book excerpt: Around the globe, ex ante evaluation of legislation has become an established rationalisation of legislative processes. Legislators, politicians, and the public at large increasingly demand new laws to have a particular effect and no unwanted side effects. Various instruments are being applied that all have in common that they must predict the effect of new legislation. Until now, most publications on regulatory impact assessment praise such instruments as being extremely useful. Scepticism, however, is in order as well. Is it not as difficult to predict the future effect of a new set of rules in our complex society as it is to predict where our society as a whole is going? The search for an answer to this sceptical question is at the heart of the book. The newly established Research Group for Methodology of Law and Legal Research at Tilburg University (the Netherlands) brought together some of Europe s top specialists in the field of ex ante evaluation of legislation, with backgrounds in law, social science, political science, and law and economics. The result of their collaborative effort is a comprehensive and critical book on the pros and cons and on the opportunities, limitations, and challenges of ex ante assessment of legislation.