IEC 61158-1:2019 (E) specifies the generic concept of fieldbuses. This document presents an overview and guidance for the IEC 61158 series 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 and showing how to use parts of the IEC 61158 series in combination with the IEC 61784 series. It also provides 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. This second edition cancels and replaces the first edition published in 2014. This edition constitutes a technical revision. This edition includes the following significant changes with respect to the previous edition: • updates of the references to and information about the IEC 61158 series, IEC 61784 1, IEC 61784 3, IEC 61784-5 series and IEC 61918 throughout the document; • new Type 25 and the related profile family CPF 20; • new Type 26 and the related profile family CPF 21.