Government regulation is necessary to the economic life of all developed countries. However the costs of regulation, in particular the cost estimates employed in the policy-making process, are often hotly debated. Drawing on recent case studies from Europe, this innovative and thoroughly accessible book examines the accuracy of regulatory cost estimates and explores in detail how these costs are calculated, the apparent relationship between ex post and ex ante calculations and why this might be.This is an objective contribution to a debate often characterised by polemic and unfounded claims. With a firm empirical basis, a wide range of case studies are presented to test theories of cost estimation which cover a diverse range of regulation in the areas of air quality and energy, industrial processes and products and agriculture and food. It will be of great interest to academics and researchers of the economics of environmental regulation and public policy. Practical suggestions for improving the accuracy of regulatory cost estimates will be of interest to a variety of economists grappling with regulatory and other impact assessments. The rationale for regulation, outlined in the book, provides a knowledge of the ideas that underpin regulation that will help non-economists (for example from regulated industries and NGOs) to engage in the wider debate about environmental regulation.