Many organisations use Environmental Management Systems (EMS) based on ISO 14001 to manage and improve their environmental performance. Certification of the EMS by an accredited third party allows the organisation and interested parties (e.g. clients, regulators) to have confidence that the system conforms to the specified standard. This Practitioner Note covers the role of accredited third party certification and some of the main factors to be considered when using certification services. This guide is primarily written in respect of ISO 14001 although parallels may be drawn with other EMS standards (e.g. EMAS, BS 8555).