This part of ISO 27145 provides an overview of the structure and the partitioning of the different parts of ISO 27145 and shows the relationship between the parts. In addition, it outlines the use case scenarios where the ISO 27145 series is used. All terminology that is common throughout the ISO 27145 series is also outlined.ISO 27145 is intended to become the single communication standard for access to OBD-related information. To allow for a smooth migration from the existing communication standards to this future world-wide communication standard, the initial communication concept is based on the ISO 15765 series, i.e. Diagnostic communication over Control Area Network (DoCAN).The intention is for the future communication concept to be based on the ISO 13400 series, i.e. Diagnostic communication over Internet Protocol (DoIP) utilizing Ethernet. In view of the usage of standard network layer protocols, future extensions to optional physical layers (e.g. wireless) are possible.ISO 27145 has been extended to defne the world-wide harmonized On-Board Diagnostics (OBD) communication standard. Based on the results of the initialization, the external test equipment determines which protocol and diagnostic services are supported by the vehicle’s emissions-related system, i.e.legislated OBD: ISO 15031 series (based on DoCAN), and- legislated WWH-OBD: ISO 27145 series (based on DoCAN and DoIP).IMPORTANT — Use cases deriving from country-specifc implementation of Global Technical Regulation (GTR) No. 5 into local legislation are not included in this part of ISO 27145.