This Practice Note considers the use of protective costs orders (PCOs) in judicial review (JR) proceedings for environmental matters, and was originally produced in partnership with Landmark Chambers. It explains the reason for special costs protection measures in environmental law, what a PCO is, and when they can be used in environmental matters. It covers access to justice and costs under the United Nations Economic Commission for Europe (UNECE) Convention on Access to Information, Public Participation in Decision-Making and Access to Justice in Environmental Matters (Aarhus Convention), the application of the Civil Procedure Rules (CPR), PCOs in Aarhus Convention claims and claims under the CPR and costs protection in cases falling outside of the CPR. It also covers the changes regarding costs protection in judicial reviews after the entry into force of sections 88–90 of the Criminal Justice and Courts Act 2015.