Environmental studies typically involve the combination of dynamic models with data sources at various spatial and temporal scales. Also, the scale of the model output is rarely in tune with the scale at which decision-makers require answers or implement environmental measures. Consequently, the question has been raised how to obtain results at the appropriate scale. Models, usually developed at the scale of a research project, have to be applied to larger areas (extrapolation), with incomplete data coverage (interpolation) and to different supports (upscaling and downscaling) to facilitate studies for decision-makers. This book gives an overview of the various problems involved, and focuses on a description of upscaling and downscaling methods that are known to exist. Furthermore, this book is the first in its kind in that it contains a decision support system that advises the practitioner on which upscaling or downscaling method to use in his specific context. This book is meant for an audience of MSc- and PhD-students, applied researchers and practitioners in soil science, hydrology, (agro) ecology, agronomy and the environmental sciences in general.