In March 2007 we were invited by the House of Lords Select Committee on Regulators to review the way that impact assessment is performed by five regulators: Ofcom; Ofgem; Ofwat; Postcomm; and the Office of Rail Regulation (ORR). This report sets out each regulator’s approach to impact assessment (Part One); reviews the quality of a sample of their impact assessment documents (Part Two); and considers the framework that regulators have established for developing impact assessment documents and how the process fits into their wider policy development cycle (Part Three).