Our world is increasingly conscious of environmental issues. In IT, one concern is that of the legacy IT infrastructure and the need to improve its sustainability. In this paper we argue that the sustainability of any IS innovation will be formally assessed as organizations and individuals consider such innovations for adoption. Therefore we propose an addition to the classic diffusion of innovation factors of a sixth factor, Relative Sustainability. Relative Sustainability can be initially operationalized using the three eco-goals identified by Watson et al, 2010: 1. Eco-efficiency measures whether an IT good or service reduces ecological impacts and resource use and is competitively priced. 2. Eco-effectiveness measures how well an IT innovation has been designed from the beginning to be sustainable. 3. Eco-equity, which measures how well the IT good or service will result in a fair distribution of resources within and between generations. Measuring eco-equity will require predictions about both initial resource use of an IT innovation (e.g., energy consumption), but also longer-term resource issues, such as final disposal of an IT product (are IT components recyclable or biodegradable, or will they pollute the environment?). We consider the case of the diffusion of cloud computing, in particular the establishment of data centers for private and public clouds. Cloud computing is selected because it represents a transformational change in how computing is done on many levels. The replacement of distributed data centers with fewer, centralized data centers delivers eco-efficiency, especially in energy and water savings and toxic disposal. Also, the new improved designs of data centers that employ a mix of technologies (including server virtualization, sensors and next-generation air- and equipment-cooling processes) and services that aid utilization of far less non-renewable resources, offer the promise of eco-equity. Finally, the massive computing power of cloud centers facilitates innovation of sustainable products delivering opportunities for eco-effectiveness.