The main objective of the IEC 61850 standard for power utility automation communication is to “provide a framework to achieve interoperability between the Intelligent Electronic Devices supplied from different suppliers” [1]. Many users expect conformance tested devices to be “plug and play” with no interoperability issues. Present experience however shows that conformance testing only reduces the number of interoperability issues and additional measures are needed to ensure cooperation of multi-vendor devices. This article is about key issues involved with creating a test facility for interoperability testing of IEC 61850 devices and systems involving different vendors. A testing strategy to ensure interoperability is presented.