Information Technology is responsible for approximately 2% of the world's emission of greenhouse gases. The IT sector itself contributes to these greenhouse gas emissions, through its massive consumption of energy - and therefore continuously exacerbates the problem. At the same time, however, the IT industry can provide the technological solutions we need to optimise resource use, save energy and reduce greenhouse gas emissions. We call this Greening IT. This book looks into the great potential of greening society with IT - i.e. the potential of IT in transforming our societies into Low-Carbon societies. The book is the result of an internationally collaborative effort by a number of opinion leaders in the field of Greening IT.