Forests must be measured if they are to be managed and conserved properly. This book describes the essential principles of modern forest measurement, whether using simple hand-held equipment or sophisticated satellite imagery. It particularly focuses on measuring forest biomass over large forest areas, a key aspect of climate change studies, as well as the volumes of wood that are commercially available. Written in a straightforward style, it will be accessible to anyone who works with forests, from the professional forester to the layperson. It considers not only how and why forests are measured but also the scientific basis of the measurements taken.