National tests, public examinations, and vocational qualifications in England are used for a variety of purposes, including the certification of individual learners in different subject areas and the accountability of individual professionals and institutions. However, there has been ongoing debate about the reliability and validity of their results. This debate prompted the Office of Qualifications and Examinations Regulation (Ofqual), the regulator of qualifications and examinations in England, to initiate its Reliability of Results Programme in 2008 to investigate the reliability of results from regulated assessments. The purpose of this programme was to gather evidence to develop regulatory policy on assessment reliability in order to improve the national assessment systems in England. This paper provides a brief introduction to the Reliability Programme, discusses its main findings to date and their implications, and explores the impact of the development of regulatory policy on reliability for regulated assessments in England. (Contains 6 tables and 4 figures.)