This document specifies the generic concept of fieldbuses. This document also presents an overview and guidance for the IEC 61158 series by: • explaining the structure and content of the IEC 61158 series; • relating the structure of the IEC 61158 series to the ISO/IEC 7498-1 OSI Basic Reference Model; • showing the logical structure of the IEC 61784 series; • showing how to use parts of the IEC 61158 series in combination with the IEC 61784 series; • providing explanations of some aspects of the IEC 61158 series that are common to the type specific parts of the IEC 61158-5 including the application layer service description concepts and the generic fieldbus data types.