Smart Cities are a key mechanism for facilitating sustainability – be that in the use of resources (e.g. energy, water), the running of city infrastructure (e.g. transport) or in terms of social policy (e.g. politics). Using our experience of a Smart City project, MK:Smart, we describe what role citizen-led innovation could have in promoting long-term sustainable change. Beyond this we detail some of the barriers to success we have identified in the hope that design patterns might help us address these challenges