This chapter presents the essential information about data communication protocols used in digital substations (DS) according to the IEC 61850 standard. The chapter begins by explaining abstract communication models and services, as reflected in IEC 61850-7-2, 7–3, and 7–4, with an emphasis on mapping communication services to specific data transmission protocols. It then provides information on how to integrate devices into the PCS (Process Control System) within the framework of IEC 61850 using the MMS protocol, which facilitates client–server communications in the form of generating reports, event logs, and operational control of equipment in the DS. Detailed descriptions are provided for the GOOSE and Sampled Values protocols, which were introduced for the first time by the IEC 61850 standard. The application areas of GOOSE and Sampled Values protocols, their general characteristics, abstract models, and their mapping to specific communication protocols are discussed. Specific attention is given to the GOOSE protocol’s features for use in digital substations. Similarly, for Sampled Values, the configuration of the process bus and time synchronization for analogue signal converters are examined.