OpenStack and open source technologies generally hold the promise of standardization and interoperability through mass market adoption. Unfortunately standards, protocols, and most importantly, software, does not guarantee interoperability. Interoperability only comes through market pressure from customers who need a solution to work. In the mid 1990s IPSEC VPN products all implemented the same standard and protocols, yet interoperability between vendor products took a very long time to occur. In this talk we’ll cover why OpenStack and open source is no panacea, where OpenStack is today in terms of interoperability with itself and others, discuss the trajectory of interoperability projects within the OpenStack community such as DefCore and RefStack, and provide a detailed blueprint for how to measure and test for interoperability between all kinds of clouds, both public and private.