Open source has not only helped free users from vendor lock-in; it has untapped new sources of innovation and enabled new opportunities for collaboration. These and other open source values are now serving to revolutionize cloud computing--indeed, to make it possible in the first place. Yet, it's not a simple literal translation. Open source protections such as licenses have different meanings, especially in public clouds. And new aspects of and potential threats to software freedom, like APIs, are central to cloud computing, whether on-premise or otherwise.