In his judgment for the majority in Gemma O’Doherty and John Waters v Minister for Health, the chief justice upheld the decision of the Court of Appeal to refuse leave to the applicants to bring judicial review proceedings challenging the constitutionality of Covid “lockdown” measures. But the Supreme Court appeal in Gemma O’Doherty was about much more than the constitutionality or otherwise of those measures. O’Donnell CJ’s judgment addresses itself to very general questions in respect of rights-based challenges to legislation in the Irish constitutional system. It assesses the standing of “the proportionality test” in Irish constitutional law. It considers the question as to where the “onus of proof” in respect of proportionality might lie. And it explores the role of policy-based or scientific evidence in such challenges. The majority judgment in Gemma O’Doherty thus offers something of a roadmap to Irish lawyers and judges in respect of how to approach the tasks of arguing and adjudicating upon rights-based challenges to legislation in this particular constitutional ecosystem. And it is a judgment that is rooted fundamentally in a concern for legitimacy.