This paper assesses the communication, information and functional requirements of Virtual Power Plants (VPPs). A conceptual formulation of the interoperability requirements is presented as well as a comparative study of their fulfillment by state-of-the-art communication techniques. VPP requirements are then mapped against services and information models of IEC 61850 and CIM power utility automation standards. Proposals are given for extensions of the IEC 61850 standard to enhance the interaction between VPP controller and the distributed energy resources. Finally the methodology and concepts are applied to a specific VPP consisting of hydro and wind plants, solar PV and storage facilities. Several applications to provide grid services from the proposed VPP in an existing 50 kV grid are covered. The implementation of the VPP communication and control architecture in the SCADA of demonstration plant is also presented.