A guide to the requirements for obtaining a Norwich Pharmacal order (NPO), and the grounds on which a respondent may challenge or vary an NPO. Among other issues, the note considers the mere witness rule, the test whether the respondent is involved in the wrongdoing and the extent to which a respondent may withhold disclosure of privileged or confidential documents. This note provides an essential guide to the issues taken into account when applying for Norwich Pharmacal relief or when responding to an NPO.