This book is just a beginning. It seeks to address the issues related to the evaluation of sustainable development within the built environ- ment and to provide a way forward. It is about how we can recognise, structure and assess all those factors that affect whether a development is sustainable in the medium to long term. It is also about how we try to balance these factors and how this contributes to our understanding of sustainability. It is not exhaustive as the authors believe there is still much to learn and to develop but it is hoped that it will provide another step towards a better approach to the subject.