What makes a city sustainable? Is it a question of limits or scale - can a city be too big, can a community be too small to be sustainable? Or is it the most energy-efficient state-of-the-art green buildings and recycling programs that make a city sustainable? Or is it about good transit, walkable neighbourhoods and locally-produced foods, goods and services, or diversity? Of course, collectively, sustainability incorporates all of these - and in isolation, none of these! Indeed, the deeper and more subtle conditions for sustainable cities remain largely unaddressed. It is really quite simple, as we have learned more and more about the meaning of sustainable development. Sustainable development is development that integrates ecological, social and economic decision-making. Communities can be defined not only by place, but also as communities of practice, professional affiliation, shared interests and networks, and space, including, virtual communities. In addition, community usually implies some sort of regularly interacting system of networks, what we pointy-headed academics refer to as social capital. Thus, sustainable development is essentially the reconciliation of ecological, social and natural capitals; specifically the dynamic reconciliation of these capitals that a community defines as critical to its development.