ISO 15257:2017 defines five levels of competence (detailed in Clause 4) for persons working in the field of cathodic protection (CP), including survey, design, installation, testing, maintenance and advancing the science of cathodic protection. It specifies a framework for establishing these competence levels and their minimum requirements. Competence levels apply to each of the following application sectors: - on-land metallic structures; - marine metallic structures; - reinforced concrete structures; inner surfaces of metallic structures containing an electrolyte. These application sectors are detailed in Clause 5. ISO 15257:2017 specifies the requirements to be used for establishing a certification scheme as defined in ISO/IEC 17024. It is not mandatory to apply all of the levels and/or application sectors. This certification scheme is detailed in Annexes A, B and C.