This Practice Note examines the duty of candour in judicial review, with a particular focus on the defendant’s obligations. All parties to judicial review proceedings are under a general duty of candour to disclose facts and information relevant to the proceedings. The general duty of candour places a particular burden on public authorities to evidence relevant information in order for the court to evaluate the facts, without being reminded to do so. Failure to disclose, even where the information will assist the claimant’s case, can lead to specific disclosure requests and affect the outcome of the case including punitive cost orders.