Over the last decade, external assessments of organizational effectiveness have played an increasingly pivotal role in the regulation of UK local authorities. Unlike most approaches to evaluation, which are concerned with the implementation and outcomes of policies, programmes or interventions, these assessments are concerned primarily with internal organizational processes. And in contrast to traditional forms of public services inspection, which focus on specific services, they seek to judge the capacity of an organization as a whole. Inspectors in England, Scotland and Wales have taken different approaches to assessments of local authorities, but in all three cases their judgements have excited considerable interest among policy-makers, achieving a much higher level of utilization than is usual for evaluative activities and being credited with leading to significant improvements in public service organizations. There are, however, important questions about the validity of the measures they use and the sustainability of this approach to driving public services improvement.