This publication is essentially an introduction to the process of energy auditing, supported by practical examples. The first part provides a phase-by-phase description of how to approach assessment, measurement, evaluation and implementation, stressing the ongoing nature of the task. The approaches described draw on the extensive experience of energy efficiency management in the international oil industry, but the content focuses mainly on the small- to medium-sized operations in many sectors of industry, particularly in developing countries. In order that the benefits of energy efficiency assessment as described in Part I can be considered in their global context, Part II examines the science of climate and climate change and covers the significance of human activity, including the use of fossil fuels. Part II draws extensively on a UK Department of Environment publication and reflects the perspectives offered in the science section of the IPCC report for which the United Kingdom assumed responsibility.