Urban sustainability indicators are tools that allow city planners, city managers and policymakers to gauge the socio-economic and environmental impact of, for example, current urban designs, infrastructures, policies, waste disposal systems, pollution and access to services by citizens. They allow for the diagnosis of problems and pressures, and thus the identification of areas that would profit from being addressed through good governance and science-based responses. They also allow cities to monitor the success and impact of sustainability interventions. A myriad of indicator tools have been advanced and tested in real cities by various organisations and research groups. These tools are available for implementation by others, and usually include aspects of sustainable development beyond environmental dimensions only, such as public health and services, governance, income, business opportunities, and transport. The challenge for urban authorities is deciding which tool best addresses the needs and goals of a particular city, which would be easy to implement and which are worth the financial and human effort. In some cases, a selection of different tools may be desirable for a city home to a small population; in others, a large city may want to join an established global programme of indicators. This report aims to provide local government actors and stakeholders with a concise guide to the best currently available indicator tools for sustainable cities, focusing on the environmental dimension. The tools summarised herein were chosen based on scalability and ease of use, and the positive and negative aspects of each for different situations of cities are addressed, along with real-world case studies that demonstrate how they can be implemented. In Chapter 2 and Chapter 3, the concept of urban metabolism is clarified in the context of environmental, social and economic sustainability, and information on how to choose an appropriate indicator set is provided. Chapter 4 reviews simple, scalable indicator tools, and other useful indicator programmes and approaches are covered in Chapter 5. It is important to note that an exhaustive list of all available tools, and a comprehensive evaluation of each is beyond the scope of this report. However, as far as possible, further reading suggestions and contact details of the relevant organisations that could assist with implementation or information is provided. In-depth Report 12. Produced for the European Commission DG Environment by the Science Communication Unit, UWE, Bristol.