This chapter analyses, from a comparative perspective, the law of judicial review of administrative action as it relates to factual error. The analyses is conducted in four common law jurisdictions (Australia, Canada, England and Wales, and Ireland), which have a ‘filial relationship’ as part of the common law tradition of controlling administrative action through the ordinary courts. The chapter outlines the traditional approach to judicial review of factual error in the four jurisdictions, characterized by limited judicial oversight of issues of fact. Next, the chapter describes the recent evolution in the law of judicial review of factual error. Although the evolutionary path has not led to the same destination in each jurisdiction, there has been increased judicial willingness to examine alleged factual errors in judicial review proceedings. However, the factors which have influenced the evolution of the law are different in each jurisdiction.