This part of IEC 62746-10@ OpenADR 2.0 (this document)@ specifies a minimal data model and services for demand response (DR)@ pricing@ and distributed energy resource (DER) communications. This document can be leveraged to manage customer energy resources@ including load@ generation@ and storage@ via signals provided by grid and/or market operators. These resources can be identified and managed as individual resources with specific capabilities@ or as virtual resources with an aggregated set of capabilities. This document specifies how to implement a two-way signaling system to facilitate information exchange between electricity service providers@ aggregators@ and end users. The DR signalling system is described in terms of servers (virtual top nodes or VTNs)@ which publish information to automated clients (virtual end nodes@ or VENs)@ which in turn subscribe to the information. This document provides application-level service communication that can be used to incentivise a response from a customer-owned DER. Price and DR signals over the internet allow indirect control of customer-owned devices that otherwise would not be available. This document's services are independent of transport mechanisms. For the purposes of interoperability@ this document provides basic transport mechanisms and their relevant interaction patterns to address different stakeholder needs. In addition@ this document specifies cyber security mechanisms required for data confidentiality@ integrity@ authentication and message-level security@ in order to provide non-repudiation and mitigation of cyber security risks. The services make no assumption of specific DR electric load control strategies that can be used within a DR resource or of any market-specific contractual or business agreements between electricity service providers and their customers. This document provides a clear set of mandatory and optional attributes within each of the services to meet broader interoperability@ testing and certification requirements. All necessary XML schema are included in Annex E.